MINERAL IDENTIFICATION KEY II
by Alan Plante,  Donald Peck  &  David Von Bargen

We wish to make this key available to one and all in the hope of correct identification of minerals in collections, rock gardens, and on windowsills everywhere. You may copy it, or any part of it, for non-commercial, personal use.

We thank Lloyd Brown, David Jacobson, and Alfred Ostrander. Their excellent advice and encouragement in this project was extremely helpful. ©  2003,  Alan Plante, Donald Peck & David Von Bargen

Table of Contents

Section 1       Section 2

Introduction

This Mineral Key is designed and intended for use on-line. The premise behind this Key is similar to that of the identification keys found in some fern and wildflower books: Key diagnostic properties are used to direct users to tables where further information on "likely suspects" is found.  That information is then used to narrow down the choices to one or a few of the most likely minerals.  Then more detailed information can be found in a mineral guide book or website databases such as Mindat, Webmineral, or the MSA's "Handbook of Mineralogy" in order to make a final determination of the mineral in the sample.

Unlike most keys for wildflowers, this system for the identification of minerals is limited – both in scope and applicability. Only a couple hundred of the most common or "usually seen" mineral species are covered. Users may well come across rare species which are not covered here. The system also requires good enough samples of the minerals to perform the tests in the sections describing mineral species. It is probably not useful for the identification of micro-crystal samples. Still, it can help narrow down the search by eliminating the more common species as possibilities. If a sample of some unknown mineral does not "key out" to one of the common species, then further testing and research to determine its identity might be worth while. But the user is cautioned that every possible effort should be made to key the sample out using this Key before looking elsewhere for help. Many common minerals have varied habits and other characteristics which might lead one to suspect a sample to be something rare, when in fact it is a common species in one of its less-prevalent forms. A careful examination of guide book information may allow one to identify the unknown sample.  Resorting to such things as sending samples in to a lab should be the last thing one does with an unknown. You should be quite certain that it is a rare species, one not covered here or in a mineral guide. Tests should be done on a fresh and unweathered surface if possible (don't break a good crystal, when an inconspicuous surface will do for testing).

Often a single series of tests may not key the user in to the correct identification. The odds of making a correct identification will be increased if tests are repeated. Take several streaks, especially if a sample is proving difficult to get a streak from, test the hardness more than once – and do tests both ways, trying to scratch the known hardness tool with the mineral and trying to scratch the mineral with the tool. If possible, when examining samples for cleavage, look at several samples – and try to use fresh breaks, cleavages which you – not nature – have produced. It is often a good idea to examine small cleavage surfaces using a 10X lens. If the first try at determining a hardness is unsuccessful or ambiguous, perhaps the second, third, or fourth will do the trick. The same holds for other tests. Such diligence to repetitive procedure usually pays off where a single try does not.

Finally, if the first run through the tests doesn’t seem to be leading you to the correct identification – try again from scratch. A second run through the entire procedure may do the trick – maybe rethinking some aspect of the tests, such as whether or not the sample really has a metallic luster. In the end, care should lead one to the correct identification for species covered in this Key. Also, practice may not always make perfect – but in the case of mineral identification the more you practice the better you will get at it. So try running samples of known species through the procedure to get a feel for how the key leads one step-by-step towards an identification. Practice, practice, practice…

[ Table of Contents ] [ Introduction ] [ Identification Kit ] [ Mineral Properties ] [ Environments & Associations ] [ In Conclusion ] [ The Mineral ID Key ]

A Simple Identification Kit

In order to use this identification key you will need to assemble an "Identification Kit". Here’s what you’ll need: Most of these items are for testing hardness, and there are more listed than the key itself requires.  But when you get to the sections and have specific minerals in mind, the extra hardness tools will help you in determining whether or not your unknown has the specific hardness of one of the minerals listed.  A hardness table is provide below showing the relative hardness of the items listed.  The streak plate is used for obtaining a colored (or not) powder streak of the mineral.  Many minerals give a different powder streak color than the mineral itself.  (Such as black hematite giving its characteristic "rust red" streak.)  The candle stub or lighter is used for doing basic fusibility tests – will a chip fuse in the flame?  The tweezers keep your fingers from getting burned doing the fusibility test!  A magnet is used for testing whether or not a sample is magnetic.  A loupe is often necessary for examining broken mineral surfaces to check the cleavage.  And figuring out what mineral you have would be a waste of time if you don’t label the sample – and forget what it is by the time you get around to looking at it again.

The items can be kept in a leather pouch, a small plastic box – or anything that’s the right size and durable.  But it is a good idea to keep the kit items together in some sort of container.  Then you always know where to find them when you need them.

[ Table of Contents ] [ Introduction ] [ Identification Kit ] [ Mineral Properties ] [ Environments & Associations ] [ In Conclusion ] [ The Mineral ID Key ]

Mineral Properties

Luster  Hardness  Streak  Cleavage  Fusibility  Specific Gravity  Habit  Tenacity  Color  Luminescence  Radioactivity  Magnetism 

In order to use this Key and the test kit described above, you need to understand some basic properties of minerals. The most important are: luster, streak, hardness, and cleavage. It is also good to know a bit about such things as specific gravity, fusibility, mineral "habits", and the types of mineral "environments" different minerals are likely to be found in – what types of rock, under what physical conditions. Brief discussions of the most important properties follow below. Any good mineral book should have more detailed sections discussing them, and the user of this Key is advised to get one and read it before working with this Key and the kit.

Luster:  A mineral’s luster is the overall sheen of its surface – it may have the sheen of polished metal, or that of an unpolished metal that is pitted by weathering – or it may have the sheen of glass, or look dull or earthy, etc.  Luster should not be confused with color:  A brass-yellow pyrite crystal has a metallic luster, but so does a shiny grey galena crystal .  Quartz is said to have a glassy (or vitreous) luster, but its color may be purple, rose, yellow, or any of a wide range of hues.  The different types of luster referred to are: Metallic, having the look of a polished metal; Submetallic, having the look of a metal that is dulled by weathering or corrosion; and Non-metallic, not looking like a metal at all.  Nonmetallic luster is divided into several sub-types:

Certain minerals with a resinous or adamantine luster – such as sphalerite and cinnabar respectively – can appear submetallic.  Care needs to be taken in deciding which of these lusters a particular mineral has. Since getting the luster right is the first critical step in keying out a mineral, always do your best to determine what the luster of a "mystery mineral" is before going on to the next step.   Return to Key: Step 1

Hardness is a mineralogical term denoting how resistant a mineral is to being scratched.  It should not be confused with a mineral’s overall "toughness."  (Diamond is the hardest known mineral, but it has a perfect cleavage and breaks easily along that cleavage.)  Relative Hardness is used in identification by comparing the hardness of the mineral to that of items with known hardness.  Mohs Scale of Relative Hardness is used, and is presented here with the addition of a few common materials of known hardness added:

1:     Talc (softest)
2:     Gypsum
2½:     Fingernail
3:     Calcite or Copper Penny
4:     Fluorite
5:     Fluorapatite
5+:     Pocket Knife
5½:     Window Glass
    
6:     Orthoclase  (or Microcline)
6½:     Steel File
7:     Quartz
8:     Topaz
9:     Corundum
9-9½:     Carborundum
10:     Diamond (hardest)

One tests for Relative Hardness by scratching the surface of a crystal or cleavage face with an item of known hardness – and vice versa, scratching the item of known hardness with a sharp point, edge, or grain of the mineral being tested.  Whenever possible, the test should be done both ways – first trying to scratch the sample, then trying to scratch the item of known hardness, such as scratching a crystal face with a knife point and then trying to scratch the knife blade with the point or a sharp edge of the crystal.  Since some minerals may leave a powdered streak on the item being scratched (or the known hardness item may leave a streak on the sample) one must rub the "scratch" with a finger to see if it is really a scratch or just a powder streak that rubs off.  If a mineral produces a powder streak on the item being scratched then it is probably softer than that item.  (Conversely, if the item leaves a streak on the sample it is softer than the sample.)

Since the "scratch test" is very important to the identification of minerals every effort should be made to get a positive result – be sure that the correct hardness is determined.  With some samples, it may take several tries before one can safely conclude the sample’s hardness.
 Return to Key: Step 2   Return to Key: Step 3      Return to Key: Step 5      Return to Step 7   Return to Step 10   Return to Step 14

Streak is simply the color of a mineral powder.  Many minerals have a different color when powdered than they do in crystal or massive forms. The color may be entirely different, or it may be a different shade. Quite a few minerals give a powder streak that is lighter in color than the whole crystal or massive pieces. A streak is usually obtained by dragging a sharp edge, grain, or point of a crystal across a streak plate – which is simply an unglazed piece of porcelain tile, such as those used in bathrooms and kitchens. (If you get your streak plate from a home improvement shop be sure what you get is unglazed porcelain – not plastic or some other material.) A porcelain streak plate has a relative hardness of about 6½. So minerals of that hardness and greater can not be tested on it – they’ll only scratch it. Some geologists use a steel file to test the streak of minerals with a hardness of 6 to 6½.

Streak plates tend to end up covered with traces of mineral powder in various colors. They can be "refreshed" by sanding them with fine emery sandpaper – 220 grit or higher. Do not use a coarser grit, as it will roughen the surface of the streak plate.

Some minerals can be difficult to get a good powdered streak from. As with other tests, repetition usually pays off. Always try to use a sharp edge or point, rather than just dragging the mineral across the streak plate willy-nilly. While some soft minerals give a streak easily no matter how you drag them, others will not streak well unless you use a small surface area of the mineral to get the streak. Get in the habit of looking for and using a sharp edge, grain, or the point of a crystal.
Return to Key: Step 4

Cleavage refers to the way some minerals break along certain lines of weakness in their structure.  Mica is a good example – breaking along very closely spaced flat planes that yield thin "sheets."  Calcite is another good example, breaking along three different planes that yield blocky fragments that look like a rectangular box that has been warped – called a "rhombohedron" or, simply, "rhomb."  Galena breaks along three planes at right angles to one another, producing true cubes as fragments.

Cleavages are described in terms of their quality - how smoothly the mineral breaks - and their difficulty - how easy, or how hard, it is to produce the cleavage.  The quality of cleavages are perfect, imperfect, distinct, good, fair, and poor.  The difficulty is described as easy, hard, and difficult to produce.  By way of examples, the micas have a perfect cleavage in one direction that is easy to produce; calcite has a perfect cleavage in three directions that is also easy to produce; the feldspars have a perfect cleavage in one direction that is easy to produce and a good cleavage in another direction that is hard to produce; and diamond has a perfect cleavage in four directions that is easy to produce.  Sphalerite has perfect cleavages in six directions, some of which are easy to produce, others hard - hence you won't always see all six cleavage surfaces in any given sample of the material.

Cleavage may also be described in terms of crystallographic type:

These are usually referenced to what are called crystallographic forms, usually using a shorthand known as Miller Indices.  This Key does not get that advanced, but the guides many collectors use often have this information in them.

The main thing that needs to be considered in the identification of minerals is whether or not a sample has a cleavage – many minerals don’t, breaking without producing smooth flat surfaces.  Next is whether or not there are two or more cleavage surfaces present at angles to one another and, if so, the quality of the various cleavages.  Where two or more cleavage surfaces are present, it then becomes important to figure out which crystal form they represent – cubic, prismatic, and so on.  This is usually done by "guestimating" the angles between cleavage surfaces.  Some are easy to see, like galena with its three perfect cleavages at 90 degrees to one another being cubic.  Others can be hard to determine and may require measurement of the angles.  A device called a contact goniometer can be handy for doing this. It is simply a protractor with an adjustable arm on it that is used to lay along one cleavage surface while the base of the protractor is laid across another.  More information on this can be found in some field guides and most mineralogy texts.  One can also make simple line drawings on a sheet of paper of the various angles common to minerals and keep the sheet in your guide.  This can be used  for making "eyeball comparisons" with the angles between cleavage surfaces on samples.

By-and-large, cleavages at 90 degrees to one another indicate a cubic form, cleavages at 120 and 60 degrees in the same sample indicate a rhombohedral form, and cleavages at acute to obtuse angles over long surfaces indicate a prismatic form – such as in feldspars.  Nearly rectangular or sharp angles in prismatic minerals may indicate a Pyroxene Group mineral or one of the Feldspars, while more open angles – approximately 120 degrees – may indicate an Amphibole Group mineral.  (Not all do, but these three groups are common and frequently seen, so seeing these types of cleavages is likely to mean you have one of them.)  A single cleavage at 90 degrees to a crystal face indicates a basal form – such as in micas.  See a good guide book for further information.

 

Parting:  Some minerals which do not exhibit cleavage do have a characteristic that is similar, called parting.  It occurs in minerals that are crystallographically twinned, or which have been stressed by pressure.  It is usually not as well, or regularly, developed as cleavage surfaces - resembling an indistinct or poorer cleavage, and it is hard to difficult to produce in specimens.  Perhaps the three best examples of it are the basal parting seen in the pyroxene minerals, the micaceous appearing parting in "specular" hematite, and the rhombic parting seen in corundum.  But the fact is that for all practical purposes it looks just like cleavage - you only know it isn't when you read in books that what you are seeing is due to twinning or pressure.

 Return to Step 6     Return to Step 8   Return to Step 11   Return to Step 13   Return to Step 14

Fusibility is a measure of how much heat it takes to melt a mineral into a globule, or at least to melt the sharp edge of a sharp splinter and make it round over.  Quite a few minerals are easily fusible in the flame of a candle or typical cigarette lighter:  A small, sharp, splinter held in the flame either melts into a globule or its edges round over easily.  So this can be a handy test to do; and a candle or lighter is easy to obtain and keep handy for use in testing.  Such minerals are said to have a fusibility of "1" or "2" – though for our purposes the degree of difficulty with which a mineral fuses is not particularly important.  Either it does or it doesn’t.

Other fusibility tests can be performed in the home workshop, using a blowtorch.  It takes some practice, but it should not be too hard for most people to become proficient at these tests.
Return to Step 9

Density and Specific Gravity are not properties easily determined, requiring special equipment; but a result of them, which might simply be called "heft" can come in handy:  The denser a mineral is, the heavier it is per given volume.  A 1 inch cube of galena is noticeable heavier in the hand than a 1 inch cube of pyrite.  A barite crystal of the same size as other similar glassy crystals is likely to feel noticeably heavier.  So do cerussite and anglesite crystals.  So a mineral’s "heft" can be a clue to its identity.  With a little practice a collector can become quite proficient at judging the relative weight of minerals and using that to help establish a sample’s identity.

In the home lab or workshop, specific gravity (S.G.) can be a very useful property in identifying minerals.  Collectors should learn about S.G. and test for it routinely when working on "mystery minerals" at home.  Any good guide or text covers this topic and methods of testing.  Probably the easiest is using a standard triple-beam balance, available from any scientific supply house – or perhaps through the local high school chemistry lab.

Habit is the general appearance a mineral tends to have – whether it is found as blocky crystals, long slender ones, or aggregates of some type, etc.  If the crystals are glassy but cubic in shape you know they aren’t quartz.  If they are rounded like a soccer ball you know they aren’t tourmaline.  And so on…

Distinct crystals may be described as:

Quartz and tourmaline crystals are prismatic, actinolite is often bladed, millerite is acicular.

Groups of distinct crystals may be described as:

Compact parallel or radiating groups of individual crystals may be described as: A mineral aggregate composed of scales or flakes may be described as: A mineral composed of grains is simply said to be granular. Granular minerals may be composed of rounded or semi-rounded grains, or of angular grains.

A few other descriptive terms are:

A wide variety of other terms are also used to describe mineral habits.  Usually they refer to loose associations with common objects or concepts and are readily apparent when the term is used in context with the form present in the mineral at hand.

Tenacity refers to a mineral’s resistance to breaking, bending, or otherwise being deformed.  A mineral may be brittle, easily broken or crushed to powder; malleable, easily hammered into thin sheets (such as copper or gold); sectile, easily cut with a knife; flexible, easily bent without breaking and then staying bent; or elastic, bending but resuming its original shape once pressure is released.

Tenacity is particularly useful in telling some of the metallic minerals apart.  Gold is malleable, pyrite (and most other look-a-likes) is not. Gold is also sectile and – in thin sheets – flexible.  Galena is brittle, while platinum is malleable and sectile.

Flexibility and elasticity can be useful with minerals that are commonly found as flakes or acicular crystals.  Chlorite flakes and thin crocoite crystals can be bent, and they will stay bent.  Mica sheets bend and then snap back to their original shape when released.

Color is often a double-edged sword in mineral identification:  There are many minerals which have distinctive colors; but there are also many which come in a variety of hues.  And the same color can be seen in several different species. So one needs to use color as a criteria with care.  That "malachite-green" mineral may not be malachite…  That brass-yellow metallic mineral may not be pyrite…  It is always a good idea to try and get a powdered streak from any colored mineral and compare it with descriptions of the streaks for the likely suspects you have in mind.  It is also always wise to consider the habit of the mineral in conjunction with the color.  A green prismatic crystal with a hexagonal cross-section is more likely to be elbaite than malachite.  A brassy wedge-shaped crystal is more likely to be chalcopyrite than pyrite.

Color, in general, should never be taken as diagnostic by itself.  While it may be for certain species, more likely than not it isn’t.  Else the job of mineral identification would be made easy.

Play of Color can be more helpful than the color itself.  Characteristics such as opalescence, iridescence, chatoyancy and asterism are peculiar to a limited number of species, or varieties of species.

Opalescence, as the word suggests, refers to an opal-like play of light, reflections off the mineral producing flashes of color that may appear somewhat like a patch-work of different "grains" of color that aren’t really there:  Move the sample minutely and the color disappears from that spot.  It is sort of like taking a pearly luster to the nth degree.

Iridescence Iridescence is the production of a rainbow of colors caused by interference of light in thin films of different refractive indices and varying thickness (the oil sheen on water is an example of this). Minerals with metallic luster, such as bornite and chalcopyrite are good examples of minerals which exhibit iridescence.  A couple of cases where it does not involve metallic minerals are the way fracture surfaces in quartz may show it, and the way some fluorite crystals may exhibit it on the surfaces of their faces.  Another exception is the type of iridescence known as  labradoresence or schiller, found in labradorite and a very few other minerals.

Chatoyancy is the play of light off closely packed parallel fibers or parallel inclusions in cavities.  The light reflects along lines – which may be straight or curved – giving the mineral a somewhat silky appearance.  This characteristic is seen in such minerals as "satin spar" gypsum, "tiger’s eye" (fibrous crocidolite replaced by quartz), and chrysoberyl.

Asterism is a type of chatoyancy in which the fibers or inclusions reflecting the light are arranged in a pattern radiating outwards from a point producing a star-like pattern.  This is most often seen in rubies and sapphires, and sometimes in phlogopite mica that has rutile inclusions.

Luminescence is the emission of light by a mineral other than the reflected light of the sun or a lamp – the mineral "glows" due to some other reason. The usual reason is reaction to ultraviolet light, though X-rays and electrons may produce it as well. The types of luminescence seen in minerals are fluorescence and phosphorescence – two closely related phenomena. Fluorescence results from electrons orbiting the mineral’s atoms being excited by ultraviolet light; the electrons "absorb" the energy and jump to higher orbits, then fall back to their original orbits – giving off light in the visible spectrum as they do. Phosphorescence is basically the same thing, but continues for a time after the source of excitation is removed, giving off energy as visible light more slowly. The fact is that most fluorescent minerals exhibit phosphorescence to some extent, though it usually can only be seen under careful lab conditions.  Only a very few minerals phosphoresce well enough to see in a simple darkened room, and the phenomenon is usually rather short lived.

Fluorescence is a useful field identification tool for collectors who have UV lights (and a thick blanket when in the field) Many localities have at least a couple of fluorescent minerals, and some – like Franklin/Ogdensburg, New Jersey, USA – have a wealth of them. Where they are present, the UV light can be put to use in identifying them. Some animals such as scorpions also will fluoresce so be careful when picking up a fluorescent object in the field.

Radioactivity is another property that, while not too common, is found in some minerals and can be useful in identification.  Collectors who have a Geiger counter may find it useful at certain localities, particularly pegmatites – where many of the more common radioactive minerals are found – as well as sedimentary rocks in the Western United States.

Magnetism is not too prevalent in minerals, but in those that do exhibit it the property can be useful in making an identification.  Having a small but strong magnet handy is a good idea, even if it only gets used now and then. The only strongly magnetic mineral collectors are likely to come across is, of course, magnetite.  Some other minerals that may exhibit weak magnetism are pyrrhotite, ilmenite and franklinite.

A couple of other electrical properties found in minerals are piezoelectricity and pyroelectricity, though they are not common. They are also rather difficult to test for  and won’t be covered here. Anyone interested in them can find information in most texts on mineralogy.

Acid Reactions: Reaction to acids is a property that can be used to help identify some carbonate minerals and zeolites. Dilute hydrochloric acid will react with carbonates such as calcite to give off appreciable bubbles of carbon dioxide in a relatively short period of time. Minerals such as dolomite have to be powdered (increasing surface area) to give an observable reaction. The zeolites will be attacked by acids, especially those zeolites that contain less silica. These minerals will become frosted in 5-10 minutes and will either dissolve or create a silica gel when grains are left in the acid for 24 hours. 

ACIDS ARE DANGEROUS!  Even weak acids can harm soft tissue, such as eyes and lungs. As with dealing with any hazardous substance, be sure to read, understand, and follow the labels and Material Safety Data Sheets for the proper methods for storing, using, disposing and appropriate emergency procedures for these materials. Always wear full-coverage splash proof lab goggles to protect your eyes when working with acids. Also have adequate ventilation when working with hydrochloric acid, especially the commonly available commercial strength solutions.

 

Luster  Hardness  Streak  Cleavage  Fusibility  Specific Gravity  Habit  Tenacity  Color  Luminescence  Radioactivity  Magnetism

[ Table of Contents ] [ Introduction ] [ Identification Kit ] [ Mineral Properties ] [ Environments & Associations ] [ In Conclusion ] [ The Mineral ID Key ]

Mineral Environments & Associations

Where a mineral is found – the type of rock in which it is found – and with what it is found – the other minerals that occur with it – can be as important to identifying the mineral as its physical properties. While there is not room for much of this information in the Key, the collector should pay close attention to it when they encounter it in field guides or other reference works.

Mineral Environments refers to the "geologic environments" in which minerals occur – the types of rocks in which they are found.  While some minerals occur in two or more environments, others tend to be restricted to a single environment.  If you think you have found the mineral kyanite in a sedimentary sandstone and see that it is a mineral formed by metamorphic processes you’ll know it can’t be kyanite.  Try celestite…  If you think you have found topaz in a cavity in basalt and read that it is largely restricted to pegmatite you’ll know it isn’t topaz.  And so on.

On a smaller scale, environments can vary over the volume of a single deposit.  A lode of copper ores may have an oxidized zone (gossan) , a supergene enriched zone, and a deep primary zone. Each zone tends to produce distinct mineral assemblages.  And figuring out in which zone a mineral formed leads to learning about mineral associations.

Mineral Associations are simply that – what minerals occur with one another in what environments.  Such as minerals like malachite and brochantite most often being found with chalcopyrite and pyrite.  Or secondary phosphate minerals being associated with triphyllite or lithiophilite.  If you think you’ve found vivianite in a pegmatite, but there is no triphyllite around, maybe that isn’t what you have…

So it is always a good idea to pay attention to environmental information and any associations described. Sometimes an identification can be nailed down with that information – or one or more likely suspects eliminated by it.  As stated above, this information is as important as the physical properties of the minerals themselves.

Information about the minerals that have been found at a particular location is often available either on the web, in various "hobby" publications, the scientific literature, and in publications from the various state and national (United States) geological surveys. These mineral lists often contain descriptions of the mineral habits found at a locality, and can be an invaluable help in determining what mineral(s) you have. This is another reason why good record keeping about the locality where a specimen is from is extremely helpful.

[ Table of Contents ] [ Introduction ] [ Identification Kit ] [ Mineral Properties ] [ Environments & Associations ] [ In Conclusion ] [ The Mineral ID Key ]

In Conclusion

As hinted at in the sections above, the collector needs to be careful about depending too much on any one or two properties or tests. While a mineral’s color, or hardness, or streak, etc., may suggest a likely culprit, a systematic approach – followed methodically – is much more likely to bring you to an accurate conclusion. Many collectors are well aware of the unreliability of "sight identifications" – deciding what a mineral is just by looking at it. Yes, many common minerals can be identified that way with experience – but many more can’t, and every now and then something so identified turns out to actually be something else. Even chemical and crystallographic tests have been known to fail to identify a mineral correctly. So it isn’t surprising that simpler techniques need to be used carefully in order to get the best results; and sometimes, they too fail.

Finally, while this Key should help the collector correctly identify many minerals, it won’t work all the time. Common minerals are found in uncommon forms. Some are closely mimicked by less-common or rare species. And, there is always the chance that a collector will find something that isn’t even covered by this Key. If you find yourself correctly identifying 60% of the minerals you find, you will be doing well. And the odds are that the other 40% are species not readily identified with this key – worked on in the home lab with other techniques, maybe even sent in to a professional lab in order to obtain a positive identification.

The trick is to do your best at each stage of the discovery process.

[ Table of Contents ] [ Introduction ] [ Identification Kit ] [ Mineral Properties ] [ Environments & Associations ] [ In Conclusion ] [ The Mineral ID Key ]

Organization & Redundancy

Beyond the obvious organization of the mineral listings into sections and sub-sections, there is a rough order of presentation which may help make it easier for the user to key things out.

The main order of presentation is by key features of the minerals – luster, streak, cleavage, and so on. When the key leads you to a particular sub-section based on a key feature you then have to carefully try and match your sample to one or more of the descriptions listed in that subsection. Since some of the subsections have quite a few minerals listed, an attempt has been made to organize them into groupings based on further refinements of the features. For example, if you have a non-metallic mineral with a colored streak and end up at subTable IIA you will see that the minerals are grouped according to color of streak – all the pinks to reds together, all the oranges and yellows next, and so on. Then within a particular group they are listed roughly in order of increasing hardness – softer ones first, hardest last. So you should be able to quickly eliminate anything that doesn't have the color streak of your sample and concentrate on those that do, and if you know the hardness you may be able to focus your search even further, paying closest attention to those species with the same hardness as your sample.

Another example is the way subTable IIB-1 is subdivided: all those that have cleavage in only one direction are first, then those with two cleavages, then those with three. Note that the background color in the table changes with each change in the number of cleavages. Within each group they are again listed in subgroups by color and hardness. So if you have a sample with cleavage in two directions you can quickly skip down to the listings for those and then home in by color and hardness. In places, the subdivisions go even further – like all the Amphibole Group species of similar hardness being listed together.

Hopefully this organization – which is admittedly not perfect – will help you to refine your search and focus on the most likely minerals that match the sample in your hand.

A number of minerals are listed in more than one place. For example, hematite is listed three times.  This is because it has such varied habit and differences in its properties from habit-to-habit that one might key one sample out to one place, but then key out a sample with a different habit and properties to another place. Also, some species sort of fall on the dividing line between sections of the listings. Such minerals might key out to either section, so they are listed in both. And some species may or may not exhibit prominent cleavage, keying out to different spots depending upon which is the case for the sample you have in your hand. Etc…

Where there is more than one mineral in the name field, this signifies that there is a solution series with more than one end member or that the compound can exist in two different crystal classes. These series are created when one element can substitute for another  at a particular place in the crystal. To fully characterize these minerals, a chemical analysis is usually required (which is beyond the scope of this key).

Hopefully this feature of the key will enhance the odds of keying out any given sample – no matter what it's particular properties may be.

Table of Contents     The Mineral ID Key

The Mineral Identification Key

Step 1: Is the Luster Metallic or Submetallic?
Yes - [Go to Section I: Metallic or Submetallic Luster Key, Step 2]
No - [Go to Section II: Nonmetallic Luster Key (Soft), Step 4]

Table of Contents     Luster

Section I: Minerals with a Metallic or Submetallic Luster

Step 2: Will the mineral leave a mark on paper?  (Hardness less than 2½?)
Yes - [Go to Table IA]
No - [Go to Step 3]

Table of Contents       Step 1   Hardness

Section I: Minerals with a Metallic or Submetallic Luster & Hardness Greater than 2½

Step 3: Can the mineral be scratched by a knife? (Hardness less than 5½?)
Yes - [Go to Table IB]
No - [Go to Table IC]

Table of Contents      Step 1       Step 2       Hardness 

Section II: Minerals with a Non-Metallic Luster

Step 4: Does the mineral have a definitely colored streak? (Leaves a colored powder streak on unglazed porcelain?)
Yes - [Go to Table IIA]
No - [Go to Step 5]

Table of Contents      Step 1       Step 3    Streak

Section II: Minerals with a Non-Metallic Luster

Step 5: Can the mineral be scratched by a fingernail? (Hardness less than 2½?)
Yes - [Go to Step 6]
No - [Go to Step 7]

Table of Contents       Step 1     Step 4      Hardness

Section II: Minerals with a Non-Metallic Luster & Hardness Less than 2½

Step 6: Does the mineral have prominent cleavage?
Yes - [Go to Table IIB-1]
No - [Go to Table IIB-2]

Table of Contents       Step 1      Step5    Cleavage

Section II: Minerals with a Non-Metallic Luster & Hardness Greater than 2½

Step 7: Can the mineral be scratched by a copper penny? (Hardness less than 3?)
Yes - [Go to Step 8]
No - [Go to Step 10]

Table of Contents       Step 1       Step5      Hardness

Section II: Minerals with a Non-Metallic Luster & Hardness Greater than 3

Step 8:  Does the mineral have a prominent cleavage?
Yes - [Go to Table IIC-1]
No - [Go to Step. 9]

Table of Contents    Step 7    Cleavage

Section II: Minerals with a Non-Metallic Luster, Hardness Greater than 2½ & No Prominent Cleavage

Step 9:  Will a thin splinter fuse in a candle flame? (Fusibility of 1?)
Yes - [Go to Table IIC-2a]
No - [Go to Table IIC-2b]

 Table of Contents     Step 8      Fusibility

Section II: Minerals with a Non-Metallic Luster & Hardness Greater than 3

Step 10:  Can the mineral be scratched by a knife? (Hardness less than 5½?)
Yes - [Go to Step 11]
No - [Go to Step 12]

Table of Contents   Step 7      Hardness

Section II: Minerals with a Non-Metallic Luster & Hardness Less than 7

Step 11: Does the mineral have a prominent cleavage?
Yes - [Go to Table IID-1]
No - [Go to Table IID-2]

Table of Contents   Step 10   Cleavage

Section III: Minerals with a Non-Metallic Luster & Hardness Greater than 5½

Step 12 Can the mineral be scratched by a sharp quartz point? (Hardness less than 7?)
Yes - [Go to Nonmetallic Luster Key (Hard): Step 13]
No - [Go to Nonmetallic Luster Key (Hard): Step 14]

Table of Contents     Step 10     Hardness

Section III: Minerals with a Non-Metallic Luster & Hardness Less than 7

Step 13 Does the mineral have a prominent cleavage?
Yes - [Go to Table IIIA-1]
No - [Go to Table IIIA-2]

Table of Contents   Step 12     Cleavage

Section III: Minerals with a Non-Metallic Luster & Hardness Greater than 7

Step 14  Does the mineral have a prominent cleavage?
Yes - [Go to Table IIIB-1]
No - [Go to Table IIIB-2]

Table of Contents    Step 12     Cleavage

Table IA:  Minerals with Metallic or Submetallic Luster &  Hardness of less than 2½: (Will readily leave a mark on paper.)
Hardness Color Streak Cleavage Name System Habit SG Notes
1+ Dark-red to Vermilion Rust-red   HEMATITE
Fe2O3		 Trigonal Ocherous masses, granular, often as a pigment – "rust" – in rocks 5.2 Exhibits a wide range of hardness depending on form; crystalline hematite is harder.
1 to 1½ Steel-grey to Iron-black Black One perfect direction (basal) GRAPHITE
C		 Trigonal May be in small hexagonal plates 2.23 Has a greasy feel.
1 to 1½ Bluish-black Black to Greenish-black One perfect direction (basal) MOLYBDENITE  MoS2 Trigonal Usually in somewhat foliated appearing masses, often leaf-like hexagonal plate 4.7 Has a greasy feel; heavier than graphite
Hardness Color Streak Cleavage Name System Habit SG Notes
1 to 2 Iron-black Black One perfect direction PYROLUSITE
MnO2		 Tetragonal May be splintery or in  radiating fibrous masses 4.7 Sometimes won’t mark paper. Most dendrites are not pyrolusite.
1½ Lead-grey Lead-grey One perfect direction NAGYÁGITE
Pb5Au(Te,Sb)4S5-8		 Orthorhombic pseudo-
tetragonal		 Usually platy masses, may be granular 7.4 to 7.5 Flakes flexible.  Rare.
1½ Steel-grey Steel-grey One perfect direction TETRADYMITE
Bi2Te2S		 Trigonal Usually in foliated to bladed masses, acute rhombohedral crystals rare 7.1 to 7.4 Flexible.  Relatively rare.
1½ to 2 Silvery-white Grey   SYLVANITE
(Au,Ag)2Te4		 Monoclinic Usually granular or in bladed aggregates, often appears as skeletal forms on rocks, resembling writing (cuneiform). 8 to 8.2 May not mark paper. Rare.
Hardness Color Streak Cleavage Name System Habit SG Notes
2 Grey-black to Lead-grey Black to Grey-black One perfect direction, two imperfect BISMUTHINITE Bi2S3 Orthorhombic In bladed crystals showing cross striations 6.78 Similar to stibnite but heavier.  Rare
2 Grey-black Bluish-black to Silvery-black One perfect direction (prismatic), two imperfect STIBNITE
Sb2S3		 Orthorhombic Usually as thick bladed crystals with striations both parallel to and across the long axis; crystals often bent or "kinked" 4.5 Fuses in a candle flame,  sometimes won’t mark paper.
2 to 2½ Grey-black to Lead-grey Black   ACANTHITE
Ag2S		 Isometric Pseudo-cubic,  usually massive 7.3 Bright-steel-grey on fresh surfaces but darkens upon exposure, easily cut with a knife (sectile).  Sometimes won’t mark paper
2 to 2½ Iron-black Iron-black STEPHANITE
Ag5SbS4		 Orthorhombic Usually massive, more rarely as short prismatic to tabular crystals 6.2 to 6.5 Rare
Hardness Color Streak Cleavage Name System Habit SG Notes
2 to 2½ Bright-red Bright-red to Deep-red One perfect direction CINNABAR
HgS		 Trigonal Usually in granular masses 8.1 Luster actually adamantine, sometimes appearing sub-metallic to metallic. May not mark paper.
2 to 2½ Brownish-red to Scarlet or Vermilion Deep Ruby-red to Bright Ruby-red One distinct direction PYRARGYRITE/ PROUSTITE
Ag3(Sb,As)S3
Ag3(As,Sb)S3		 Trigonal Prismatic, pyramidal, rhombohedral, and scalenohedral crystals , also massive, usually as complex intergrown crystal aggregates 5.57 to 5.58 Isostructural species difficult to distinguish, though pyrargyrite is usually darker in color and more common than proustite. Rare.
2 to 2½ Silvery-white Silvery-white with decidedly reddish tones One perfect direction (basal), one good  BISMUTH
Bi		 Trigonal Usually in laminated granular masses, may be arborescent or reticulated, artificial crystals in pseudo-cubic "hopper" groups 9.8 Heavy. Rare. May not mark paper.
Hardness Color Streak Cleavage Name System Habit SG Notes
2½ Brass-yellow to Silvery-white Yellowish- to Greenish-grey   CALAVERITE
AuTe2		 Monoclinic Usually granular, rarely in distinct elongated crystals 9.35 Very heavy, easily fusible in candle flame (leaving globules of gold). (May not mark paper.)  Rare.
2½ Grey-black to Black Bluish-black to Lead-grey Perfect in three directions at 90o to each other GALENA
PbS		 Isometric Usually in cubic crystals or masses exhibiting cubic cleavage, also in granular masses. 7.6 Sometimes won’t mark paper
2 to 3 Black Black One imperfect direction POLYBASITE
(Ag,Cu)16Sb2S11		 Monoclinic, pseudo-
hexagonal		 Usually massive or in crude pseudo-hexagonal plates 6.1 to 6.2 Rare

Table of Contents   Return to Step 2

Table IB: Minerals with Metallic or Submetallic Luster & Hardness greater than 2½, but less than 5½: (Will not easily mark paper, but can be scratched with a pocket knife.)
Hardness Color Streak Cleavage Name System Habit SG Notes
1 to 2 Iron-black Black One perfect direction PYROLUSITE
MnO2		 Tetragonal May be splintery or in radiating fibrous masses 4.7 Will sometimes mark paper.
1½ to 2 Silvery-white Grey   SYLVANITE
(Au,Ag)Te2		 Monoclinic Usually granular or in bladed aggregates, often appears as skeletal forms on rocks, resembling writing (cuneiform) 8 to
8.2		 May mark paper.
Rare
1½ to 2 Metallic-blue, tarnishes to blue-black Black One perfect direction (basal) COVELLITE
CuS		 Trigonal Platy masses or thin six-sided platy crystals 4.6 May be somewhat iridescent, turns metallic-purple when wet. Will sometimes mark paper.
Hardness Color Streak Cleavage Name System Habit SG Notes
2 Bluish-black to Silvery-black Grey-black One perfect direction (prismatic), two imperfect STIBNITE
Sb2S3		 Orthorhombic Usually as thick bladed crystals with striations both parallel to and across the long axis; crystals often bent or "kinked" 4.5 Fuses in a candle flame. Will sometimes mark paper.
2 to 2½ Deep Ruby-red to Bright Ruby-red Brownish-red to Scarlet or Vermilion One distinct direction PYRARGYRITE/ PROUSTITE 
Ag3(Sb,As)S3
Ag3(As,Sb)S3		 Trigonal Prismatic, pyramidal, rhombohedral, and scalenohedral crystals , also massive, usually as complex intergrown crystal aggregates 5.58 (pyrargyrite), 5.57 (proustite) Isostructural species difficult to distinguish, though pyrargyrite is usually darker in color and more common than proustite, fusible in a candle flame. Rare.
2 to 2½ Grey-black to Lead-grey Black   ACANTHITE
Ag2S		 Isometric Pseudo-cubic, usually massive 7.3 Bright steel-grey on fresh surfaces but darkens upon exposure, easily cut with a knife (sectile). Will usually mark paper.
Hardness Color Streak Cleavage Name System Habit SG Notes
2½ Bluish-black to Lead-grey Grey-Black to Black Perfect  in three directions at 90o to each other GALENA
PbS		 Isometric Usually in cubic crystals or masses exhibiting cubic cleavage, also in granular masses 7.6 Will usually mark paper. Most common heavy mineral.
2½ Brass-yellow to Silvery-white Yellowish to Greenish-grey   CALAVERITE
AuTe2		 Monoclinic Usually granular, rarely in distinct elongated crystals 9.35 Very heavy, easily fusible in a candle flame (leaving globules of gold). May mark paper. Rare.
2 to 3 Grey-black Black One good direction JAMESONITE
Pb4FeSb6S14		 Monoclinic Dense clusters or carpets of fibrous to acicular crystals; very delicate! 5.5 to 6.0 Fuses easily in a candle flame.
Hardness Color Streak Cleavage Name System Habit SG Notes
2½ to 3 Grey-black Grey to Black   BOURNONITE
PbCuSbS3		 Orthorhombic Usually in stout prismatic crystals often as intergrown clusters with twinning exhibited by re-entrant angles 5.8 to 5.9 Fuses easily in a candle flame
2½ to 3 Steel-grey, may tarnish to black on exposure Grey to Black   CHALCOCITE
Cu2S		 Monoclinic, pseudo-
orthorhombic		 Usually in compact masses, crystals tabular to stoutly prismatic, often with a pseudo-hexagonal outline, vertically striated. 5.7  
2½ to 3 Dark metallic Blue to Black Black   DIGENITE
Cu9S5		 Isometric Usually massive as small to tiny irregular grains, very rarely as octahedral crystals 5.5 to 5.7 Very similar to chalcocite, but much rarer in non-microscopic sizes.
2½ to 3 Steel-grey, tarnishes metallic blue Dark steel-grey   STROMEYERITE
AgCuS		 Orthorhombic, pseudo-
hexagonal		 Usually massive, granular, rarely as pseudo-hexagonal prismatic crystals 6.2 to 6.3 Rare.
Hardness Color Streak Cleavage Name System Habit SG Notes
2½ to 3 Lead-grey Brown to brownish-grey One distinct direction BOULANGERITE
Pb5Sb4S11		 Monoclinic Usually massive as fibrous bundles, crystals usually needle-like mats, prismatic crystals rarer 6.0 to 6.3 Thin acicular crystals flexible. Rare.
2½ to 3 Dark-red to Vermilion Dark-red One perfect direction CINNABAR
HgS		 Trigonal Usually massive, crystals uncommon and usually rhombohedral, often as penetration twins 8.10 Luster actually adamantine, appearing metallic, heavy.
2½ to 3 Copper-red on fresh surfaces, tarnishes to brown or black Coppery-red, shiny   COPPER
Cu		 Isometric Usually in irregular masses, large grains, wires, and crude dendritic crystals, crystals usually octahedral and malformed, may be cubic or other Isometric forms 8.9 Malleable.
2½ to 3 Golden-yellow, shiny, becoming paler with increased Ag content - electrum variety Golden-yellow, shiny   GOLD
Au		 Isometric Usually massive in irregular grains, nuggets, "leaves" and "flakes", crystals often wires crudely dendritic or as malformed octahedrons 15.0 to 19.3 Malleable, very heavy! Rare. Distinguished from pyrite – "fools gold" – by its malleability, softness and weight.
2½ to 3 Silvery-white,
tarnishes black		 Silvery-white, shiny   SILVER
Ag		 Isometric Usually massive as irregular grains,  wires, and dendritic crystals 10.5 Malleable, heavy. Rare.  May mark paper.
Hardness Color Streak Cleavage Name System Habit SG Notes
3 Grey-black Black One perfect (prismatic), two distinct, and one indistinct direction ENARGITE
Cu3AsS4		 Orthorhombic Usually in bladed masses 4.4 Crystals vertically striated
3 Brownish-bronze on fresh surfaces, tarnishing to metallic purple, iridescent ("peacock ore") Grey-black   BORNITE
Cu5FeS4		 Orthorhombic,
pseudo-
tetrahedral		 Crystals usually pseudo-cubic, usually massive 5.1 Thin splinters fusible in a candle flame, giving a brittle magnetic globule.
3 to 3½ Brass-yellow Black, sometimes with a greenish tinge   MILLERITE
NiS		 Trigonal Usually in radiating groups or mats of needle-like to hair-like crystals 5.5 Slender crystals usually have a greenish tinge
3 to 3½ Steel-grey Steel-grey One indistinct direction ZINKENITE
Pb9Sb22S42		 Hexagonal Usually massive, also in columnar and radiating fibrous aggregates of needle-like crystals 5.2 to 5.3 Rare
3 to 3½ Tin-white Silvery-grey, shiny One perfect, one distinct, and one imperfect direction ANTIMONY
Sb		 Trigonal Usually massive, foliated, or granular, rarely as pseudo-cubic or thick tabular crystals 6.6 to 6.7 Very brittle. Rare
Hardness Color Streak Cleavage Name System Habit SG Notes
3 to 4½ Steel-grey, may tarnish dead black upon exposure Black (may be Brownish-black)   TETRAHEDRITE/
TENNANTITE
(Cu,Fe)12Sb4S13
(Cu,Fe)12As4S13		 Isometric Usually massive or granular, crystals uncommon and usually pseudo-tetrahedral 4.6 to 5.1 End members difficult to distinguish without subtle tests – an S.G. above 4.7 is conclusive for tetrahedrite.
3½ Tin-white, tarnishing to Dark-grey Grey-black One perfect (basal) ARSENIC
As		 Trigonal Usually found in botryoidal fibrous masses 5.7 Heated in candle flame it gives off white fumes that have a strong garlic odor (poisonous!) Rare
3½ to 4 Brownish-bronze to Bronze-yellow Black No cleavage but large grains exhibit an octahedral parting PENTLANDITE
(Fe,Ni)9S8		 Isometric Usually massive in granular aggregates 4.6 to 5.0 Resembles pyrrhotite but is not magnetic, often mixed with pyrrhotite
3½ to 4 Brass-yellow, often iridescent Black   CHALCOPYRITE
CuFeS2		 Tetragonal Usually massive, crystals blocky tetrahedrons or wedge-shaped. 4.1 to 4.3 Often mixed with pyrite, making a hardness test inconclusive; distinguished from pyrite by softness and shape of crystals.
3½ to 4 Brown to Black Brown Good  in one direction, poor in another direction WURTZITE
ZnS		 Hexagonal Usually massive and as banded botryoidal crusts, more rarely as pyramidal hemimorphic crystals 4.0 to 4.1 Rare
Hardness Color Streak Cleavage Name System Habit SG Notes
3½ to 4 Dark-brown to black, sometimes Olive-yellow or Red ("Ruby Jack") to Reddish-black Dark to Light-brown: streak usually lighter than the color of the sample Perfect  in six directions, three directions usually prominent SPHALERITE
ZnS		 Isometric Usually in compact crystalline masses, crystals usually blocky pyramidal, appearing tetrahedral 3.9 to 4.1 Luster actually resinous, appearing metallic or submetallic
3½ to 4 Ruby-red to Reddish-brown Brownish-red   CUPRITE
Cu2O		 Isometric Usually massive, crystals usually cubes or octahedrons 6.0 Luster may be adamantine rather than metallic in crystals
3½ to 4 Black Green One perfect direction ALABANDITE
MnS		 Isometric Usually massive or granular. 4.0 to 4.1 Rare
Hardness Color Streak Cleavage Name System Habit SG Notes
4 Brownish-bronze to Bronze-yellow Grey-black   PYRRHOTITE
Fe1-xS		 Monoclinic
pseudo-
hexagonal		 Usually massive, crystals as pseudo-hexagonal plates 4.6 to 4.7 Magnetic, though may be weak
4 Steel-grey to Iron-black Black Indistinct  in two directions STANNITE
Cu2FeSnS4		 Tetragonal Usually massive, rarely as pseudo-octahedral crystals 4.3 to 4.5 Rare
4 Steel-grey to Iron-black Dark reddish-brown to Black One perfect, two good directions MANGANITE
MnO(OH)		 Monoclinic, pseudo-
orthorhombic		 Usually in radiating fibrous masses, crystals often grouped in bundles. 4.3 Often associated with pyrolusite; distinguished from that species by its significantly greater hardness
4 to 4½ White to Steel-grey Grey, shiny   PLATINUM
Pt		 Isometric Usually massive in irregular grains or nuggets, crystals rare and usually malformed cubes 14 to 19 Malleable, very heavy!  Very rare. Distinguished from gold by its color.
Hardness Color Streak Cleavage Name System Habit SG Notes
5 Steel-grey Black One perfect direction GLAUCODOT
(Co,Fe)AsS		 Orthorhombic Usually massive, more rarely as prismatic crystals in cruciform penetration twins 5.9 to 6.1 Rare; alloclasite, monoclinic, is dimorphous with glaucodot and difficult to distinguish from it, but is probably even rarer
5 Yellowish or reddish-brown Pale-brown to white Variable: may be good in one direction and poor to good in another direction MONAZITE
(Ce,La,Nd)PO4		 Monoclinic Usually massive, granular, may be in crude large crystals 4.6 to 5.3 (approx.) Luster usually resinous to waxy, but may be adamantine and may appear sub-metallic
5 to 5½ Dark-brown to Black:  color black in ferberite brown in hübnerite Dark-brown to Black: streak darkens with increasing Fe content One perfect direction FERBERITE/
HÜBNERITE
("Wolframite" series)
(Fe,Mn)WO4
(Mn,Fe)WO4		 Monoclinic Usually massive, granular, crystals tabular to bladed with vertical striations 7.0 to 7.5 S.G. above about 7.3 indicates ferberite, lower indicates hübnerite
5 to 5½ Pale Copper-red to Pinkish silvery-white, tarnishing to Dark-grey or Black Black   NICKELINE
NiAs		 Hexagonal Usually massive, crystals rare and usually pyramidal, often malformed, may also be reticulated or arborescent 7.78 May be coated with green "nickel bloom" (annabergite).
5 to 5½ Dark brown to Black Yellow-brown or Yellow-ocher One perfect direction GOETHITE
(pronounced "Ger-ta-ite.")
FeO(OH)		 Orthorhombic Usually in radiating botryoidal aggregates, mammillary, or stalactic 4.37  
Hardness Color Streak Cleavage Name System Habit SG Notes
5½ Dark-brown to Black Iron-black to Brownish-black   CHROMITE
FeCr2O4

(Magnesiochromite is closely related, S.G. 4.2, Rare.
Manganochromite, H. 6½, is even rarer.)

 Isometric Usually massive, rarely as octahedral crystals 4.6 Luster usually pitchy, submetallic, usually associated with peridotite rocks and accompanied by green or yellow alteration products.
5½ to 6½ Dark-brown to Steel-grey to Black Rust-red or Indian-red   HEMATITE
Fe2O3		 Trigonal Usually massive in radiating, reniform, or micaceous aggregates 4.8 to 5.3 Usually harder than a knife, but some forms can be softer. (See under Sections IA & IC.)

Table of Contents    Return to Step 3

Table IC: Metallic or Submetallic Luster and Hardness greater than 5½: (Can not be scratched by a knife.)
Hardness Color Streak Cleavage Name System Habit SG Notes
4 to 5½ Black or
Dark greenish or Yellowish-brown		 Pale yellowish or Brownish   BETAFITE
(Ca,Na,U)2(Ti,Nb)O6(OH)		 Isometric Massive (metamict) Approx. 4 to 6 (variable) Luster usually sub-metallic, but may be resinous to vitreous, highly radioactive
5 to 5½ Pale Copper-red to Pinkish Silvery-white, tarnishing to Dark-grey or Black Black   NICKELINE
NiAs		 Hexagonal Usually massive, crystals rare and usually pyramidal, often malformed, may also be reticulated or arborescent 7.78 May be coated with green "nickel bloom" (annabergite)
5 to 5½ Dark-brown to Black,
color black in ferberite, brown in hübnerite		 Dark-brown to Black One perfect direction FERBERITE/
HÜBNERITE 
("Wolframite" series)
(Fe,Mn)WO4
(Mn,Fe)WO4		 Monoclinic Usually massive, granular, crystals tabular to bladed with vertical striations 7.0 to 7.5
above about 7.3 indicates ferberite, lower indicates hübnerite		 Streak darkens with increasing Fe content
5 to 5½ Dark-brown to Black Yellow-brown or Yellow-ocher One perfect direction GOETHITE
(pronounced "Ger-ta-ite.")
FeO(OH)		 Orthorhombic Usually in radiating botryoidal aggregates, mammillary, or stalactic 4.37  
5 to 5½ Dark-brown to Black, Dark yellowish-brown to Greenish-brown, Dark reddish-brown Pale yellowish or Brownish   MICROLITE
(Na,Ca)2Ta2O6(O,OH,F)		 Isometric Usually massive,
granular, crystals octahedral		 5.90-6.42 Luster usually resinous to vitreous, but when resinous may appear sub-metallic, may contain some U and be radioactive
5 to 5½ Brown to Black or Dark yellowish-brown Light-brown to Yellowish-brown   PYROCHLORE
(Na,Ca)2Nb2O6(OH,F)·nH2O		 Isometric Usually massive, granular, crystals usually octahedral, modified by the cube 4.45-4.90 Luster usually resinous to vitreous, but when resinous may appear sub-metallic, usually contains some U and is radioactive Distinguished from microlite by its lower S.G.
Hardness Color Streak Cleavage Name System Habit SG Notes
5 to 6 Black Black to Dark-brown   ROMANECHITE
(Ba,H2O)2(Mn4+Mn3+)5O10		 Orthorhombic Usually massive, botryoidal or stalactic 3.7 to 4.7 Distinguished from similar Mn minerals by its greater hardness
5 to 6 Black to Silvery-black Black to Dark-brown   ILMENITE
FeTiO3		 Trigonal Usually as platy massive or granular, crystals rare, thick tabular or acute rhombohedral 4.72 May be weakly magnetic
5 to 6 Deep blood-red Black to Dark-brown or Reddish-brown Perfect  in two directions PYROPHANITE
MnTiO3		 Trigonal Usually in fine-grained, scaly, masses 4.54  
Hardness Color Streak Cleavage Name System Habit SG Notes
5½ Tin-white or Silvery-white Black One perfect direction COBALTITE/
GERSDORFFITE
(Co,Ni)AsS
(Ni,Co)AsS		 Isometric Usually massive, granular, cubic and pyritohedral crystals (cobaltite) or octahedral and pyritohedral crystals (gersdorffite) 6.3
(cobaltite),
5.9
(gersdorffite)		 Difficult to distinguish end members without chemical tests, S.G. may help for samples close to the ideal end members.
5½ Tin-white or Silvery-white Black Two distinct directions, poor in one direction SKUTTERUDITE/
NICKEL-SKUTTERUDITE 
(Co,Ni)As2-3
(Ni,Co,)As2-3		 Isometric Usually massive, crystals cubes or cubo-octahedral 6.5
to 6.9
(skutterudite – nickel-skutterudite)		 High end S.G. indicates the skutterudite end member, otherwise difficult to distinguish from one another.
5½ Black Black to Dark-brown   URANINITE
UO2		 Isometric Usually massive 9.0 to 9.7 ("Pitchblende"), luster actually "pitchy", may be botryoidal, radioactive
5½ Brownish-black Dark-brown   CHROMITE
FeCr2O4		 Isometric Usually massive, granular 4.6 Luster actually "pitchy", often with green alteration products
5½ Pale copper-red Red-brown   BREITHAUPTITE
NiSb		 Hexagonal Usually massive, crystals rare, tabular 7.59 to 8.23 Rare
5½ to 6 Tin-white or Silvery-white, tarnishing Brown or Bronzish Black One distinct direction ARSENOPYRITE
FeAsS		 Monoclinic Usually massive, granular, crystals pseudo-orthorhombic prismatic, usually in cruciform twins or star-shaped trillings 6.0 to 6.2 Has garlic odor when ground or pounded – poisonous arsenic fumes
5½ to 6 Brown, Yellowish-brown, Reddish-brown; Dark-brown to Iron-black; White to Grayish-white or Yellowish-white One indistinct direction BROOKITE
TiO2		 Orthorhombic Usually tabular, elongated and striated crystals, commonly pyramidal or pseudohexagonal 4.08 to 4.18 Found in alpine veins in gneiss and schist. Also found in contact metamorphic and hydrothermal veins
5½ to 6 Brown, Yellowish-brown, Reddish-brown, Indigo, Black; Geenish, Pale lilac, Gray, rarely Colorless White to Pale yellow  Two perfect  directions ANATASE
TiO2		 Tetragonal Usually  pyramidal or tabular 3.79 to 3.97 Found in alpine veins in gneiss and schist as a secondary mineral. 
5½ to 6 Dark-brown to Steel-grey to Black Rust-red or Indian-red   HEMATITE
Fe2O3		 Trigonal Usually massive in radiating, reniform, or micaceous aggregates, crystals rhombohedral 4.8 to 5.3 Usually black and usually harder than a knife.  (See under Sections IA & IB.)
Hardness Color Streak Cleavage Name System Habit SG Notes
6 Black Black   MAGNETITE
Fe3O4		 Isometric Massive or in octahedral crystals 5.18 Strongly magnetic
6 Black Black to Dark-brown One distinct direction COLUMBITE/
TANTALITE
(Fe,Mn)(Nb,Ta)2O6		 Orthorhombic Usually massive platy, or as thick tabular crystals 5.2 to 6.76
(ferrocolumbite)
7.95
(ferrotantalite)		 A complex solid solution series exists within the Columbite-Group; distinguishing between species is difficult without subtle chemical tests. S.G. may be indicative for some species but not definitive. Columbite/tantalite series is now broken down into the four end-member minerals - ferrocolumbite, manganocolumbite, ferrotantalite and manganotantalite
6 Brownish-black Dark-brown   FRANKLINITE
(Fe,Zn,Mn)(Fe,Mn)2O4		 Isometric Usually massive, granular, or as octahedral crystals 5.15 May be slightly magnetic. Rare outside of Franklin, N.J., USA
Hardness Color Streak Cleavage Name System Habit SG Notes
6 to 6½ Brass-yellow Black (may be greenish-black)   PYRITE
FeS2		 Isometric Massive or in striated cubic, pyritohedral, or octahedral crystals, may be twinned 5.0 Most common brass-yellow metallic mineral
6 to 6½ Brass-yellow Black (may be greenish-black) One distinct direction MARCASITE
FeS2		 Orthorhombic Usually massive, granular, crystals usually "cockscomb" clusters or radiating fibrous aggregates 4.9 Difficult to distinguish from pyrite without tests unless good crystals are present.
6 to 6½ Dark-brown to Black Pale-brown One distinct direction RUTILE
TiO2		 Tetragonal Usually in prismatic crystals, vertically striated, often needle-like as inclusions in silicate crystals, particularly quartz 4.2 to 4.25 Anatase and brookite are closely related species, but rarer.

Note: The Betafite-Microlite-Pyrochlore Group and Subgroups are complex, species can be difficult to tell apart. S.G. and radioactivity may be indicative for some species, but are rarely definitive.

Table of Contents   Return to Step 3

Table IIA: Minerals with a Nonmetallic Luster, Definitely Colored Streak, and Hardness 1 to 6:
Streak Hardness Color Cleavage Name System Habit SG Notes
Rust-red to Indian-red 1+ to 6½ Dark-brown to Steel-grey to Black   HEMATITE
Fe2O3		 Trigonal Usually massive in radiating, reniform, or micaceous aggregates  4.8 to 5.3 Hardness and S.G. lower in earthy massive materials, harder and denser in crystals and crystalline materials, crystals usually 5½ to 6½ with a metallic to sub-metallic luster
Pink 1½ to 2½ Pale-pink to Red Perfect in one direction ERYTHRITE
Co3(AsO4)2.8H2O		 Monoclinic Usually as earthy crusts or powdery coatings on cobalt minerals, may be reniform 2.95 Streak same color as the sample but paler. Rare. (See also annabergite, below.)
Pale-pink to Light-green 1½ to 2½ Apple-green , Grey, Pale-rose Perfect in one direction ANNABERGITE
Ni3(AsO4)2.8H2O		 Monoclinic Usually as coatings or crusts of tiny crystals, grainy-appearing, crystals bladed  3.0 to 3.23 Streak same color as sample but lighter; Rare.  (See also erythrite above.)
Red 2 Red   LITHARGE
PbO		 Tetragonal As alteration crusts on massicot (see below) 9.14 Rare
Streak Hardness Color Cleavage Name System Habit SG Notes
Bright-Scarlet-red or Vermilion to Brownish-red 2 to 2½ Dark Ruby-
red or Bright Ruby-red		 One distinct direction PROUSTITE/
PYRARGYRITE
Ag3(Sb,As)S3
Ag3(As,Sb)S3		 Trigonal Prismatic, pyramidal, rhombohedral, and scalenohedral crystals , also massive, usually as complex intergrown crystal aggregates 5.58 (pyrargyrite)
5.57 (proustite)		 Isostructural species difficult to distinguish, though pyrargyrite is usually darker in color and more common than proustite, fusible in candle flame. Rare.
Dark-red 2½ Dark-red to Vermilion One perfect direction CINNABAR
HgS		 Trigonal Usually earthy or granular, commonly impure and dark red or reddish-brown, bright-red and translucent to transparent when pure, crystals rhombohedral or tabular to short prismatic 8.10 Luster of crystals adamantine, may appear sub-metallic, heavy
Bright- to Deep-red 2½ to 3 Orange-yellow One distinct direction CROCOITE
PbCrO4		 Monoclinic Usually in prismatic crystals with an adamantine to sub-vitreous luster, as parallel to jackstraw clusters, may be hollow 5.9 to 6.1 Decrepitates (crumbles explosively) in a candle flame
Dark-red 3½ to 4 Ruby-red to Reddish-brown   CUPRITE
Cu2O		 Isometric Usually in octahedral or cubic crystals, may be in slender crystals, may also be massive 6.0  
Streak Hardness Color Cleavage Name System Habit SG Notes
Orange-or Reddish-yellow 1½ to 2 Dark-red One good direction REALGAR
AsS		 Monoclinic Usually massive, granular, coarse to fine, and as crusts 3.48 Luster resinous, easily fusible in a candle flame; usually associated with Orpiment
Orange-yellow 4 to 4½ Yellow to
Orange-yellow to Deep-red		 One
perfect direction		 ZINCITE
(Zn,Mn)O		 Hexagonal Usually massive as irregular grains or rounded masses 5.64 to 5.68 Luster sub-adamantine to sub-vitreous, fluoresces green to yellowish-green under long wave ultraviolet light. Rare outside of Franklin, N.J., USA.
Pale-yellow 1½ to 2½ Lemon-yellow One perfect direction
giving thin plates		 ORPIMENT
As2S3		 Monoclinic Usually in foliated masses or grains 3.49 Flexible, luster resinous, pearly on cleavage surfaces, easily fusible in a candle flame, usually associated with Realgar
Pale-yellow 1½ to 2½ Bright-yellow Imperfect  in three directions SULFUR
S		 Orthorhombic Usually imperfectly crystallized masses or crusts 2.05 to 2.09 Resinous to sub-vitreous luster, may appear somewhat earthy when massive or as crusts, readily burns in a candle flame giving a blue flame.
Pale-yellow 2 Sulfur-yellow   MASSICOT
PbO		 Orthorhombic Usually earthy or scaly masses 9.56 Usually replaces other Pb minerals, particularly galena, scales flexible.  Rather rare.
Streak Hardness Color Cleavage Name System Habit SG Notes
Very Pale-yellow to Yellowish-green 2 to 2½ Lemon-yellow to Greenish-yellow One perfect direction and one distinct direction AUTUNITE/
META-AUTUNITE
Ca(UO2)2(PO4)2.10-12H2O
Ca(UO2)2(PO4)2.2-6H2O		 Tetragonal/
Orthorhombic		 Usually as micaceous or scaly foliated aggregates, crystals thin or thick tabular 3.15 (autunite), 3.44 (meta-autunite) Luster vitreous to adamantine, fluoresces bright greenish-yellow. (See also torbernite/metatorbernite below, does not fluoresce.) Naturally occurring material is almost invariably meta-autunite
Very Pale-yellow, Yellowish-white (both rarely seen), White 2½ to 3 Orange-red to Ruby-red, Brownish-red to Brownish-yellow or Pale Straw-yellow   VANADINITE 
(Apatite Group)
Pb5(VO4)3Cl		 Hexagonal Usually in barrel-shaped prismatic hexagonal crystals, either long or short, may be acicular in clusters or mats ("endlichite"), and as hollow prisms– "hopper" crystals 6.88 Luster sub-vitreous to sub-resinous
Very Pale-green 2 to 2½ Emerald- to Grass-green, Apple-green, Leek-green One perfect direction and one indistinct direction TORBERNITE/ METATORBERNITE
Cu(UO2)2(PO4)2.11H2O
Cu(UO2)2(PO4)2.8H2O		 Tetragonal Usually as micaceous or scaly foliated aggregates, crystals thin to thick tabular 3.22
(torbernite), 3.70 (metatorbernite)		 Luster vitreous to adamantine, similar to autunite/meta-autunite but truly green and does not fluoresce like autunite/meta-autunite. (See also autunite/ meta-autunite above.) Naturally occurring material is almost always metatorbernite
Light-green 3 to
3½		 Dark to Bright Emerald-green One perfect direction, a second fair direction ATACAMITE
Cu2Cl(OH)3		 Orthorhombic Usually in granular cleavable masses, crystals prismatic and usually very small to microscopic 3.75 to 3.77 Fusible in a candle flame. Rare.
Streak Hardness Color Cleavage Name System Habit SG Notes
Light-green 3½ Dark Emerald-green One perfect direction, one poor direction ANTLERITE
Cu3(SO4)(OH)4		 Orthorhombic Usually as mats of tiny acicular crystals, may be granular 3.88 Vitreous luster, may appear sub-vitreous or dull in mats. Rare.
Light-green 3½ to 4 Dark Emerald-green to Bright-green   BROCHANTITE
Cu4(SO4)(OH)6		 Monoclinic Usually as crusts or mats of tiny crystals, crystals may be stout prismatic to acicular or tabular 3.97 Vitreous luster
Light-green 3½ to 4 Dark- to Bright-green One perfect direction MALACHITE
Cu2(CO3)(OH)2		 Monoclinic As either radiating fibrous masses, botryoidal to mammillary, or as slender to stout prismatic crystals, often poorly formed (and often psuedomorphic after azurite), may be crusts, or acicular stellate sprays 3.9 to 4.03 Luster adamantine to vitreous, may appear sub-vitreous to dull on surfaces of masses. Often associated with azurite
Pale Bluish-white to White or Colorless 1½ to 2 Deep-blue or Deep Greenish-blue to Bluish green One perfect direction VIVIANITE
Fe3(PO4)2.8H2O		 Monoclinic Usually as flattened to bladed prismatic crystals, often in stellate clusters or sprays, may also be granular, crusts, or reniform masses 2.68 Streak: darkens to Dark-blue or Brown after exposure, vitreous luster. Rare
Very Pale-blue to Grey or Tan 2 to 4 Pale- to Deep-blue, Blue-green, Green   CHRYSOCOLLA
Cu2H2[Si2O5](OH)4		   Usually in glassy, opaline, or porcellaneous masses or crusts, often as mats of very fine acicular crystals, may be botryoidal 1.93 to 2.40 Luster may be vitreous, waxy, porcellaneous, or dull.
Streak Hardness Color Cleavage Name System Habit SG Notes
Light-blue 2½ Azure-blue to Bright-blue   LINARITE
PbCu(SO4)(OH)2		 Monoclinic Usually as clusters or sprays of tiny elongated prismatic or tabular crystals, bladed, may also be in crusts of crudely formed crystals 5.35 Luster vitreous to sub-adamantine, easily fusible in a candle flame
Light-blue 3½ to 4 Deep Azure-blue One perfect direction AZURITE
Cu3(CO3)2(OH)2		 Monoclinic Usually as small stout prismatic crystals, may be in sprays or radiating spherical groups 3.77 Luster vitreous, may appear sub-vitreous to dull on surfaces of radiating spherical masses;  usually associated with malachite
Bright-blue 5 to 5½ Deep-blue to Medium-blue and Violet-blue One distinct direction LAZURITE
Na3Ca(Al3Si3O12)S		 Isometric Usually massive, compact to granular, crystals rare, dodecahedral 2.38 to 2.45 Luster vitreous in crystals, dull in massive material. Rare. Principal mineral found in the gem stone Lapis Lazuli
Very Pale-blue to White 5½ to 6 Light- to Medium-blue, Violet-blue,
Grey, or White		 One poor to distinct direction SODALITE
Na4(Al3Si3O12)Cl		 Isometric Usually massive granular, crystals rare, dodecahedral, octahedral. Rare 2.14 to 2.30 Luster vitreous in crystals to dull in massive material, may fluoresce orange to orange-red
Streak Hardness Color Cleavage Name System Habit SG Notes
Brown 3½ to 4 Light-tan to Dark-brown Perfect  in three directions producing rhombic fragments SIDERITE
FeCO3		 Trigonal Usually in cleavable masses, crystals usually rhombohedrons, faces curved 3.83 to 3.88 Becomes magnetic when heated in a candle flame
Brown 3½ to 4 Dark-brown to Black One perfect direction FERBERITE/
HÜBNERITE 
("Wolframite" series)
(Fe,Mn)WO4
(Mn,Fe)WO4		 Monoclinic Usually massive, granular, crystals tabular to bladed with vertical striations 7.0 to 7.5
S.G. above 7.3 indicates ferberite, lower indicates hübnerite		 Color black in ferberite, brown in hübnerite. Streak darkens with increasing Fe content
Light-brown 3½ to 4 Dark to Light-brown, Olive-brown, Reddish brown, Reddish-black Perfect in six directions SPHALERITE
ZnS		 Isometric Usually in cleavable masses, granular, crystals blocky wedge-shaped 3.9 to 4.1 May have an oily, submetallic, luster, streak usually lighter than the specimen
Streak Hardness Color Cleavage Name System Habit SG Notes
Yellow-brown to Ocher-yellow 5 to 5½ Dark-brown to Black One perfect direction GOETHITE (pronounced "Ger-ta-ite")
FeO(OH)		 Orthorhombic Usually in reniform or radiating fibrous masses, botryoidal or mammillary, also stalactic 4.4 Luster usually dull, may be submetallic.
Light-brown 6 to 6½ Reddish-brown to Black One distinct direction RUTILE
TiO2

 

 Tetragonal Usually in slender prismatic crystals with vertically striated faces, as "elbow twins" (reticulated) and "sixlings" 4.18 to 4.25 Luster adamantine, may appear submetallic, usually translucent
Brown to Black 6 to 7 Light-brown to Greyish or White One imperfect direction CASSITERITE
SnO2		 Tetragonal Usually as fibrous, reniform, or irregular masses, stream-worn nuggets, with a dull to submetallic luster, crystals usually twined, with a submetallic or adamantine luster 6.8 to 7.1 Streak usually lighter than the specimen

Table of Contents    Return to Step 4

Table IIB-1: Streak not colored, Cleavage Prominent, Hardness less than 2½: (Can be scratched with a fingernail, Streak: white or none.)
Cleavage Hardness Luster Color Name System Habit SG Notes
Imperfect in four directions (octahedral) 1-2  Vitreous to sub- vitreous Colorless to White (may be stained by impurities) SAL AMMONIAC 
NH4Cl
 		 Isometric Usually as powdery crusts around volcanic vents or in coal seams that have burned, crystals usually trapezohedral, tiny, in skeletal; or dendritic aggregates, may also be gyroidal or dodecahedral (rarely) 1.53 Very plastic (difficult to determine hardness); tastes stingingly salty. Rare.
Perfect in one direction 1 Waxy to pearly White to Grey, Sea-green, impure material may be Dark-green to Dark-grey, almost Black TALC
Mg3Si4O10(OH)2		 Monoclinic Usually as foliated masses of flakes 2.7 to 2.8 Will leave a white streak on paper, flexible, has a greasy feel. The cleavage may not be readily apparent due to foliation of the flakes.
Perfect in one direction (rarely seen)  1 Vitreous  White to Colorless ULEXITE
NaCaB5O6(OH).5H2O
 		 Triclinic Usually as masses of fibrous or fine acicular crystals, rounded 1.95 Luster vitreous on ends of cleavage pieces, silky on sides, specimens with clear ends placed on print transmit the image through the sample – you can read through it. "TV-stone."
Cleavage Hardness Luster Color Name System Habit SG Notes
Perfect in one direction, good in one direction, poor in one direction (rhombohedral) 1½ to 2 Vitreous to sub-vitreous Colorless to White or Grey NITRATINE
(Nitratite, Soda-Niter):
NaNO3		 Trigonal Usually massive, granular, crystals rhombohedral 2.24 to 2.29 White streak, easily dissolved in water, has a cooling and salty taste, easily fusible in a candle flame. Natratine and niter are difficult to distinguish from one another without tests for Na and K.
Imperfect in three directions (rhombic) 1½ to 2½ Resinous to sub-vitreous, may appear somewhat earthy when massive or as crusts Bright-yellow SULFUR
S		 Orthorhombic Usually imperfectly crystallized masses or crusts 2.05 to 2.09 Usually gives a pale yellow streak, readily burns in a candle flame giving a blue flame
Cleavage Hardness Luster Color Name System Habit SG Notes
Perfect in one direction 2 to 2½ Sub-vitreous to dull. Pale to dark Green,  almost black, may be other colors, but rarely CLINOCHLORE/CHAMOSITE
(Chlorite Group)
(Mg,Fe)5Al(Si3Al)O10(OH)8
(Fe,Mg)5Al(Si3Al)O10(OH)8		 Monoclinic Usually as aggregates of foliated flakes, may be in more compact masses of fine scales 2.6 to 2.9 Flakes or scales flexible,   Difficult to distinguish between these two end members though clinochlore tends to be the more common.
Perfect in one direction, imperfect in one direction, good in one direction (prismatic) 2 Vitreous Colorless to White or
Grey		 NITER
(Saltpeter):
KNO3		 Orthorhombic Usually as thin crusts, granular to
powdery, massive, or columnar, may be in silky tufts or delicate
acicular crystals		 2.10 White streak,  easily dissolved in water, has a cooling and salty taste, easily fusible in a candle flame. Natratine and niter are difficult to distinguish from one another without tests for Na and K.
Perfect in one direction 2 Waxy White to Grey,
darker when impure, may be Greenish		 PYROPHYLLITE
Al2Si4O10(OH)2		 Monoclinic Usually as aggregates of foliated flakes, flexible 2.8 to
2.9		 Geasy feel,   may be difficult to distinguish from talc. Cleavage not always readily apparent due to foliation.
Perfect in one direction, good in two directions
(prismatic)		 2 Sub-vitreous to pearly (on cleavage faces) to silky or dull Colorless to White or Grey (may be stained
other colors by impurities)		 GYPSUM
CaSO4.2H2O		 Monoclinic May be in compact masses without cleavage ("alabaster"), fibrous masses ("satin spar") or prismatic crystals, often twinned ("selenite") 2.32 Crystals of the selenite variety are usually clear, other varieties are usually milky
Cleavage Hardness Luster Color Name System Habit SG Notes
Perfect in three directions (cubic) 2 Vitreous to sub-vitreous Colorless
to White (may be stained by impurities)		 HALITE
(Common Salt, Rock Salt)
NaCl		 Isometric Usually as granular crystalline masses or small cubic crystals 2.17 Has a salty taste.  Halite and sylvite can be hard to tell apart, but sylvite has a more bitter taste
Perfect in three directions (cubic) 2 Vitreous to sub-vitreous Colorless to White (may be stained by impurities) SYLVITE
(Potassium Salt)
KCl

 

 Isometric Usually as granular crystalline masses or small cubic crystals 1.97 to 1.99 Has a salty taste.  Sylvite and halite can be hard to tell apart, but sylvite has a more bitter taste
Perfect in one direction 2 to 2½ Pearly on cleavage
surfaces		 White, may be Pale-
green or Pale-yellow		 MUSCOVITE
(Mica Group)
KAl2(Si3Al)O10 (OH,F)2		 Monoclinic, pseudo-
hexagonal		 Usually in "books" of thin sheets or as aggregates of foliated thin scales, crystals usually elongated stacks of sheets with a hexagonal or "diamond" cross section 2.76 to 2.88 Sheets or flakes elastic. Weathers to a golden color.
Cleavage Hardness Luster Color Name System Habit SG Notes
Perfect in one direction 2 to 2½ Pearly on cleavage surfaces White to Greenish-
white or Yellowish-brown		 PHLOGOPITE
(Mica Group): 
  KMg3(Si3Al)O10(F,OH)		 Monoclinic, pseudo-
hexagonal		 Usually as aggregates of foliated thin scales or "books" of sheets, crystals rare, usually same as for muscovite 2.86 Sheets or flakes elastic.  Difficult to distinguish from muscovite, which is much more common.
Perfect in one direction 2 to 2½ Pearly on cleavage
surfaces		 Black to Brownish-
black		 ANNITE
(Biotite Mica Group)
K(Fe,Mg)(Si3Al)O10(OH,F)2		 Monoclinic, pseudo-
hexagonal		 Usually in "books" of thin sheets or as aggregates of foliated thin scales; crystals usually same as for muscovite. 2.7 to 3.4 May give a pale brownish streak, sheets or flakes elastic. Note: Materials described previously as "biotite" have been found to constitute a solid solution series, with annite the most common member.
Perfect in one direction (rarely seen) 2 to 2½ Earthy White to Tan, may be Greyish KAOLINITE
Al2Si2O5(OH)4		 Triclinic Usually as compact earthy masses 2.6 Has an earth odor when moistened, sticks to a dry tongue
Cleavage Hardness Luster Color Name System Habit SG Notes
Perfect in three directions (cubic) 2 to 2½ Vitreous Bright-red to Pale-rose, White streak VILLIAUNITE
NaF		 Isometric Usually as small to tiny cubic crystals, sometimes modified by an octahedron, also as cleavable masses (small?) 2.79 Granular, dissolves in water: very poisonous! Rare.
Perfect in one direction 2½ Pearly on cleavage surfaces White, Grey, or Greenish-white BRUCITE
Mg(OH)2		 Trigonal Usually as foliated masses of flakes or scales (thicker than the micas) 2.39 Thin flakes flexible, sectile
Perfect in one direction 2½ Sub-vitreous to waxy, may be dull White to Colorless,
Greyish, to Yellowish or Tannish		 COOKEITE
(Chlorite Group):
LiAl4(Si3Al)O10(OH)8		 Monoclinic Usually as aggregates of tiny flakes or scales, crystals in tiny rosettes or spherical radiating clusters, may be somewhat botryoidal looking 2.58 to 2.69 Flakes or scales elastic

Table of Contents   Return to Step 6

Table IIB-2: Streak Not Colored, Cleavage Not Prominent, Hardness less than 2½: (Can be scratched with a fingernail; Streak: white or none; Cleavage absent or not obvious.)
Hardness Color Luster Cleavage Name System Habit SG Notes
1 to 2  Colorless to White (may be stained by impurities) Vitreous to sub- vitreous Imperfect in four directions (octahedral), may not be seen SAL AMMONIAC
NH4Cl		 Isometric Usually as powdery crusts around volcanic-vents or in coal seams that have burned, crystals usually trapezohedral, tiny, in skeletal or dendritic aggregates 1.53 May also be gyroidal or dodecahedral (rarely), very plastic; difficult to determine hardness, tastes stingingly salty. Rare.
1 White to
Colorless		   Perfect in one direction, may not be seen ULEXITE
NaCaB5O6(OH).5H2O		 Triclinic Usually as masses of fibrous or fine acicular crystals, rounded 1.95 Specimens with clear ends placed on print transmit the image through the sample – you can read through it. "TV-stone".
1½ to 2 Colorless to White or Grey Vitreous to sub-vitreous Perfect in one direction, good in one direction, poor in one direction (rhombohedral), may not be apparent NITRATINE 
(Nitratite, Soda-Niter)
NaNO3		 Trigonal Usually massive, granular, crystals rhombohedral 2.24 to 2.29 White streak; easily dissolved in water, luster, has a cooling and salty taste, easily fusible in a candle flame;  Natratine and Niter are difficult to distinguish from one another without tests for Na and K
Hardness Color Luster Cleavage Name System Habit SG Notes
1 to 2 White, Pale pink, Buff, Yellow, Red, Green Dull to earthy  Perfect in one direction, probably will not be seen MONTMORILLONITE
(Na,Ca)0.3(Al,Mg)2Si4O10(OH)2.nH2O		 Monoclinic Usually as compact earthy masses 2-3 Earthy odor when moistened
1½ to 2½ Bright-yellow Resinous to sub- vitreous, may appear somewhat earthy when massive or as crusts Imperfect in three directions (rhombic), may not be apparent SULFUR
S		 Orthorhombic Usually imperfectly crystallized masses or crusts 2.05 to 2.09 Usually gives a pale-yellow streak, readily burns in a candle flame giving a blue flame
2 Colorless to White or Grey Vitreous to sub-vitreous Perfect in one direction, imperfect in one direction, good in one direction (prismatic), may not be apparent NITER (Saltpeter)
KNO3		 Orthorhombic Usually as thin crusts, granular to powdery, massive, or columnar, may be in silky tufts or delicate acicular crystals 2.10 White streak; easily dissolved in water, has a cooling and salty taste, easily fusible in a candle flame;  Natratine and niter are difficult to distinguish from one another without tests for Na and K
2 to 2½ White to Tan, may be Greyish Earthy  Perfect in one direction, probably will not be seen KAOLINITE
Al2Si2O5(OH)4		 Triclinic Usually as compact earthy masses 2.6 Earth odor when moistened, sticks to a dry tongue
Hardness Color Luster Cleavage Name System Habit SG Notes
2 to 2½ Bright-red to Pale-rose Vitreous to sub-vitreous Perfect in three directions (cubic), may not be seen VILLIAUNITE
NaF		 Isometric Usually as small to tiny cubic crystals, sometimes modified by the octahedron, also as cleavable masses (small?), granular 2.79 White streak; dissolves in water:  very poisonous!  Rare.
2½ White to Colorless, Greyish, to Yellowish or Tannish Vitreous to waxy luster, may be dull. Perfect in one direction, may not be seen COOKEITE
(Chlorite Group)
LiAl4(Si3Al)O10(OH)8		 Monoclinic Usually as aggregates of tiny flakes or scales, crystals in tiny rosettes or spherical radiating clusters, may be somewhat botryoidal looking, flakes or scales elastic 2.58 to 2.69 Flakes or scales elastic

Note: There are very few common to rare non-metallic species less than 2½ in hardness which do not have at least one good cleavage. Any sample that keys out to this point and is not one of the above listed minerals needs to be re-examined.  It probably either has a prominent cleavage or is harder than 2½. Or it is a very rare to extremely rare species not covered here.

Table of Contents    Return to Step 6

Table IIC-1: Streak not colored, Cleavage prominent, Hardness 2½ to 3: (Can not be scratched by a fingernail, can be scratched by a copper penny, streak white or one.)
Cleavage Hardness Color Luster Name System Habit SG Notes
Perfect in one direction (basal) 2½ to 4 Lilac, Lavender, Greyish- to Greenish-white Pearly on cleavage surfaces LEPIDOLITE
(Mica Group)
K(Li,Al)3(Si,Al)4O10(F,OH)2		 Monoclinic, pseudo-hexagonal Usually as aggregates of tiny flakes, also as "books" of larger sheets, rarely as diamond-shaped or distorted hexagonal shaped crystals, flakes or sheets 2.8 to
3.0		 Elastic, harder than other common
micas – except for margarite (see below).
Perfect in one direction (basal) 3½ to 5 Deep to pale Lilac, Grey to White Pearly on cleavage surfaces MARGARITE
(Mica Group)
CaAl2(Al2Si2)O10(OH)2		 Monoclinic Usually as flaky aggregates or cross-grain "books" sandwiched in a matrix of chlorite-rich amphibolite schist 3.0 to 3.1 Bends little and then
breaks – "brittle mica."  Hardest of the common micas.
Cleavage Hardness Color Luster Name System Habit SG Notes
Perfect in three directions (cubic) 2 Colorless to White (may be stained by impurities) Vitreous to sub-vitreous HALITE
(Common Salt, Rock Salt)
NaCl		 Isometric Usually as granular crystalline masses or small cubic crystals 2.17 Has a salty taste.  Halite and sylvite can be hard to tell apart, but sylvite has a more bitter taste
Perfect in three directions (cubic) 2 Colorless to White (may be stained by impurities) Vitreous to sub-vitreous  SYLVITE
(Potassium Salt)
KCl
 		 Isometric Usually as granular crystalline masses or small cubic crystals 1.97 to 1.99 Has a salty taste.  Sylvite and halite can be hard to tell apart, but sylvite has a more bitter taste
Distinct in one direction (prismatic), good in a second direction
(basal) and fair to poor in a third direction (rhombic overall)		 2½ to 3 Colorless or White to Greyish-white or Greyish-brown Adamantine to sub-adamantine, may be vitreous to resinous on some surfaces ANGLESITE
PbSO4		 Orthorhombic Usually in crystalline masses, crystals usually small and tabular, rarely prismatic 6.2 to 6.4 Streak white;
Massive material may be difficult to distinguish from cerussite without testing for SO4 vs. CO3  (See cerussite below).
Cleavage Hardness Color Luster Name System Habit SG Notes
Perfect in three directions, corners 120o or 60o (rhombic) 3; but may be 2 across the top surface of prismatic crystals with a flat termination Usually Clear or White to Tan or Grey, but may be tinted many colors Vitreous to sub-vitreous CALCITE
CaCO3		 Trigonal May be in cleavable masses producing rhombs, granular masses (limestone and marble), scalenohedral ("dogtooth") crystals, rhombohedral crystals, flattened rhombohedral ("nailhead") crystals, or a wide variety of related shapes; The many varied habits of calcite crystals make this one of the species that can be tough to identify by crystal form alone. Few people, if any, are familiar with all the forms it takes.  (there are over 800 crystals forms known for this species to date…) 2.71 White streak;  clear rhombs show a doubled image of print viewed through them, effervesces in cold, dilute acid – even in vinegar or Coke to a small degree.
Cleavage Hardness Color Luster Name System Habit SG Notes
Perfect in two directions (prismatic) and fair in a third 3 Colorless, White, or Grey (may be stained other colors) Vitreous to sub-vitreous KERNITE
Na2B4O6(OH)2.3H2O		 Monoclinic Usually in cleavable crystalline masses 1.95 Splintery cleavage fragments
Imperfect in one direction (basal), distinct in another direction
(rhombic), may not be seen		 3 to 3½ Colorless to White or Greyish-white, may be tinted other colors Vitreous to sub-vitreous WITHERITE 
(Aragonite Group)
BaCO3		 Orthorhombic, pseudo-hexagonal Usually as stout prismatic twinned crystals with a hexagonal cross section, often with pyramidal terminations on both ends, more rarely as globular to botryoidal clusters, coarse fibrous aggregates, and granular 4.29 Often hazed, will effervesce in cold acid.
Perfect in two directions, imperfect to good in a third  3 to 3½ Colorless to White or Greyish-white, may be tinted other colors Vitreous and/or pearly ANHYDRITE
CaSO4		 Orthorhombic Usually in coarsely crystalline masses exhibiting a pseudo-cubic cleavage, or in granular masses with no cleavage apparent, crystals rare and usually equant or thick tabular 2.9 to
2.98		 Pseudo-cubic cleavage
Cleavage Hardness Color Luster Name System Habit SG Notes
Distinct in one direction (prismatic), good in a second direction
(basal) and fair to poor in a third direction (rhombic overall)		 3 to 3½ Colorless to White or Greyish-white, may be tinted other colors Vitreous, pearly on basal cleavage
surfaces		 BARITE
BaSO4		 Orthorhombic Usually in clusters or aggregates of platy to tabular crystals 4.5 Distinguish from Celestine by SG or a  flame test (lime green)
Distinct in one direction (prismatic), good in a second direction
(basal) and fair to poor in a third direction (rhombic overall)		 3 to 3½ Colorless to White or Greyish-white, Blue, may be tinted other colors Vitreous, pearly on basal cleavage surfaces CELESTITE (Celestine)
SrSO4		 Orthorhombic Usually in clusters or aggregates of platy to tabular crystals 3.95 to 3.97 Distinguish from Barite by SG or a flame test (bright red)

Note: The above three members of the Barite Group are most easily told apart by their S.G.s  Anglesite is noticeably heavier than the other two, barite may feel heavier than celestite.

Table of Contents   Return to Step 8

Table IIC-2a: Nonmetallic Luster; Streak Not Colored; Hardness 2½ to 3; Cleavage Not Prominent; Splinter Will Fuse in a Candle Flame.
Fusibility Color Hardness Luster Name System Habit SG Notes
Swells and fuses to a glassy
globule in a candle flame		 Usually Snow-white; Colorless to White or Greyish-white, may be tinted other colors 2 to 2½ Vitreous to resinous BORAX Na2B4O5(OH)4.8H2O Monoclinic Usually in crystalline or granular masses, crystals short
prismatic to somewhat tabular, flattened prisms		 1.7 Dissolves in water, has a sweetish, alkaline taste
Small splinters fusible in a candle flame Colorless to White, may be tinted other colors 2½ Vitreous to greasy, has an unusual greasy translucence CRYOLITE 
Na3AlF6 		Monoclinic Usually massively
crystalline to coarse granular, crystal rare and usually pseudo-cubic		 2.95 to 3.0 White streak; small clear fragments seem to disappear when placed in water (nearly identical refractive-index)
Small splinters fusible in a candle flame Colorless to White or Greyish-White, may be tinted other colors 3 to 3½ Adamantine to vitreous, may be resinous on cleavage surfaces, may also appear submetallic when dark colored CERUSSITE (Aragonite Group)
PbCO3		 Orthorhombic Usually as crystalline to granular masses, crystals usually tabular in platy clusters or aggregates, may be prismatic, rarely acicular (habit widely varied) 6.55 Cleavage distinct in one direction and good in another, but rarely seen, effervesces in warm acid. Massive material difficult to distinguish from anglesite without testing for CO3 vs. SO4. Also see strontianite

Table of Contents   Return to Step 9

Table IIC-2b: Nonmetallic Luster; Streak Not Colored; Hardness 2½ to 3; Cleavage Not Prominent; Infusible in a Candle Flame.
Color Hardness Luster Name System Habit SG Notes
White to Tan, may be Greyish 2 to 2½ Earthy KAOLINITE
Al2Si2O5(OH)4		 Triclinic Usually as compact earthy masses 2.6 Has an earth odor when moistened, sticks to a dry tongue
Colorless to White or Greyish-white, may be tinted other colors 3 to 3½ Vitreous and/or pearly ANHYDRITE
CaSO4		 Orthorhombic Usually in coarsely crystalline masses exhibiting a pseudo-cubic cleavage, or in granular masses with no cleavage apparent, crystals rare and usually equant or thick tabular 2.9 to 2.98 Pseudo-cubic cleavage
Colorless to White or Greyish-white, may be tinted other colors 3 to 3½ Vitreous to sub-vitreous WITHERITE
(Aragonite Group):  
BaCO3		 Orthorhombic, pseudo-
hexagonal		 Usually as stout prismatic twinned crystals with a hexagonal cross section, often with pyramidal terminations on both ends, more rarely as globular to botryoidal clusters, coarse fibrous aggregates, and granular 4.29 Often hazed, will effervesce in cold acid.  Has cleavage, but it may not be seen.
Colorless to White or Grey, may be tinted other colors 3½ to 4 Vitreous to sub-vitreous, silky when fibrous STRONTIANITE
(Aragonite Group)
SrCO3		 Orthorhombic Usually in granular or fibrous aggregates, may be columnar, crystals short prismatic to acicular, often pseudo-hexagonal in cross- section (Ca-rich) 3.76 Effervesces mildly in cold acids, or not at all.  Distinguished from cerussite by its notably lower specific gravity, lighter feel.  Also it is  not as common as cerussite.
Shades of Green - olive, apple, dark to blackish, often mottled 2½ to 4; rarely 5 to 6 in dense massive material Sub-vitreous to greasy luster, feels greasy ANTIGORITE/
LIZARDITE/AMESITE
(Serpentine Group)
(Fe,Mg)3(Si,Al)2O5(OH)4
Mg3(Si,Al)2O5(OH)4
Mg2Al(Si,Al)2O5(OH)4 		Monoclinic, Orthorhombic and Triclinic Usually in crystalline masses, often platy or columnar 2.4 to 2.79 (antigorite), 2.55 to 2.61 (lizardite), 2.71 to 2.80 (amesite) These serpentine minerals are almost impossible to tell apart, particularly in massive forms.  They may co-exist at the same locality. Still, information on the specific locality a specimen comes from may be the best bet for nailing down the ID.
White to Grey, Pale-green to Olive-green, Golden-yellow to Brown 2 to 3 Silky CLINOCHRYSOTILE/
ORHTOCRYSOTILE/
PARACHRYSOTILE (Serpentine Group):  Mg3Si2O5(OH)4		 Monoclinic &
Orthorhombic		 Usually in fine fibrous aggregates,
fibers often very long and "weaveable,"		 2.53 to 1.55 "Asbestos" is an industrial term for several long-fiber species (not all Serpentines) that can be made into cloth or mats.
These species are extremely difficult to tell apart, although parachrysotile is rare and not likely to be seen.  Most specimens are simply labeled with the generic term:  CHRYSOTILE
Orange-red to Ruby-red, Brownish-red to Brownish-yellow or Pale
Straw-yellow		 2½ to 3 Sub-vitreous to sub-resinous VANADINITE
(Apatite Group): 
Pb5(VO4)3Cl 		Hexagonal Usually in barrel- shaped prismatic hexagonal crystals, either long or short, may be acicular in clusters or mats ("endlichite"), and as hollow prisms - "hopper" crystals 6.88 Streak white, may be yellowish
Dark-green to Yellow-green, Yellow to Orange-Yellow, Brown, White, even Colorless 3½ Sub-vitreous to resinous PYROMORPHITE 
(Apatite Group):
Pb5(PO4)3Cl 		Hexagonal Usually in barrel- shaped, prismatic hexagonal crystals, may also be spindle- shaped, hollow – "hopper crystals"; – rarely tabular or pyramidal, crystals may exhibit concentric color or structural zones due to zoned variations in composition 7.04 White streak; difficult to distinguish from mimetite without tests for PO4 vs. AsO4.
Pale-yellow to Yellowish-brown, Orange-yellow to Orange-red, White
to Colorless		 3½ to 4 Sub-vitreous to resinous MIMETITE
(Apatite Group):
Pb5(AsO4)3Cl		 Hexagonal Usually in simple barrel-shaped prismatic crystals, rarely tabular or acicular, may be botryoidal or globular 7.28 Difficult to distinguish from pyromorphite without tests for AsO4 vs. PO4; Named for the fact that it closely mimics pyromorphite
Green to Yellow, Greenish-white, Yellowish-brown to Brown, rarely other hues 3½ to 4 Vitreous to
pearly, sometimes resinous		 WAVELLITE
Al3(PO4)2(OH,F)3.5H2O		 Orthorhombic Usually in radiating fibrous aggregates or stellate clusters, as crusts, may be stalactic 2.36 Streak white; one perfect and one distinct cleavage, but they are rarely seen, dissolves in cold acids.

Note: The above three members of the Apatite Group are difficult to tell apart when they have the color(s) of vanadinite, though usually the colors in vanadinite are deeper, more intense, than the other two.  Vanadinite has lower S.G. than the other two as well.

Table of Contents   Return to Step 9

Table IID-1: Nonmetallic Luster, Hardness Greater Than 3 but Less Than 5½, and Prominent Cleavage: (Can not be scratched by a copper penny, can be scratched by a knife, streak white or none.)
Cleavage Hardness Color Luster Name System Habit SG Notes
Imperfect in one direction (basal), may be distinct in another direction (rhombic) but usually not seen 3 to 3½ Colorless to White or Greyish-white, may be tinted other colors Vitreous to sub-vitreous WITHERITE
(Aragonite Group)
BaCO3		 Orthorhombic,
pseudo- hexagonal		 Usually as stout prismatic twinned crystals with a hexagonal cross section, often with pyramidal terminations on both ends, more rarely as globular to botryoidal clusters, coarse fibrous aggregates, and granular 4.29 Often hazed, will effervesce in cold acid.
Distinct in one direction (prismatic) 3½ to 4 Colorless to White or Grey, may be tinted other colors Vitreous to sub-vitreous or resinous ARAGONITE
(Aragonite Group)
CaCO3		 Orthorhombic Usually in prismatic crystals, sometimes flattened, often acicular, usually twinned producing a pseudo-hexagonal cross section, may also be columnar, radiating or stellate aggregates, also stalactic 2.95 Often fluorescent, pale rose, yellow or bluish-white, effervesces in cold acids. Distinguished from calcite by its greater hardness, higher S.G. and different crystal forms and habits – though some crystals may mimic the forms found in calcite.
Cleavage Hardness Color Luster Name System Habit Sp. G Notes
Perfect cleavage in one direction (prismatic) 3½ to 4 Colorless to White, may be Yellow, Brown, and other colors Vitreous, pearly on cleavage surfaces STILBITE-(Ca)
(Zeolite Group)
(Ca0.5,Na,K)9[Al9Si27O72].28H2O		 Monoclinic Usually as flattened tabular long prismatic crystals, often in sheaf-like groups ("bowties") 2.12 to 2.22 White streak; dissolves in cold acids.
Perfect cleavage in one direction (prismatic) 3½ to 4 Colorless to White, may be Grey, Yellow, Pink, and other colors Vitreous, pearly on cleavage surfaces HEULANDITE-(Ca)
(Zeolite Group)
(Ca0.5,Na,K)9[Al9Si27O72].~24H2O		 Monoclinic Commonly tabular to equant crystals, may be long-prismatic, typically coffin shaped 2.10 to 2.29 White streak; dissolves in cold acids.
Perfect cleavage in one direction (prismatic) 3½ to 4 Colorless to White Vitreous, pearly on cleavage surfaces CLINOPTILOLTE-(Ca)
(Zeolite Group)
(Ca0.5,Na,K)6[Al6Si30O72].~20H2O		 Monoclinic Usually as platy crystals, may be tabular or flattened long prismatic, commonly fine-grained, massive 2.10 to 2.17 White streak; dissolves in cold acids.
Perfect cleavage in one direction (prismatic) 4½ Colorless to White, may be Pink or Brown Vitreous to sub-vitreous STELLERITE
(Zeolite Group)
Ca[Al2Si7O18].7H2O		 Orthorhombic Usually in spheres of radiating elongated tabular crystals, often also as aggregates of scaly to platy and small tabular crystals 2.13 White streak; dissolves in cold acids.
Perfect in one direction (prismatic), may have a poor (pinacoidal) cleavage in another direction 4½ to 5½ Colorless to White, Pale-pink, Pale-yellow to Pale-brown Vitreous, pearly on some cleavage surfaces BREWSTERITE-Sr/
BREWSTERITE-Ba
(Sr,Ba)2[Al4Si12O32].10H2O
(Ba,Sr)2[Al4Si12O32].10H2O		 Monoclinic & Triclinic Usually as small tabular crystals, may be blocky or prismatic as well 2.32 to 2.45 White streak; S.G. increases with Ba content; Brewsterite-Ba is the far more common of the two.
Cleavage Hardness Color Luster Name System Habit SG Notes
Perfect  in one direction (prismatic) 5 to 5½ Colorless to White, Pale-pink, may be Grey or other colors Usually vitreous to silky in finer acicular aggregates, but may be dull or even greasy NATROLITE
(Zeolite Group)
Na2[Al2Si3O10].2H2O		 Orthorhombic Usually as long slender needles in stellate clusters or radial aggregates, may also be in jackstraw clusters 2.20 to 2.27 White streak; partially decomposed by acid, producing a white gel.
Poor in one direction, may not be seen 5 to 5½ Colorless to White, may be Yellow, Pink, or other colors Vitreous ANALCIME
(Zeolite Group)
Na[AlSi2O6].H2O		 Polymorphous (Iso., Tet., Orth., Mon., Tric., Trig.) Usually in cubic or trapezohedral crystals or fine-grained masses, more rarely in other crystal forms 2.22 to 2.63 Dissolves in cold acids
Perfect in one direction (may have a distinct cleavage in a second direction) 4 to 4½ Colorless to White or Grey, may be tinted other colors Vitreous to sub-adamantine COLEMANITE
Ca2B6O11.5H2O		 Monoclinic Usually  druzy, massive granular, equant to short prismatic crystals 2.42 Decrepitates violently in a candle flame.
Perfect in one direction (may have an imperfect cleavage in a second direction) 4½ to 5 Colorless to White or Grey, Pale-green, may also be other tints Vitreous to sub-vitreous, pearly on cleavage surfaces FLUORAPOPHYLLITE/
HYDROXYLAPOPHYLLITE
KCa4Si8O20F.8H2O   
KCa4Si8O20(OH).8H2O		 Tetragonal Crystals usually equant, blocky, may be stout tabular, more rarely prismatic, commonly striated 2.33 to 2.37 It is impossible to tell the two end members apart without subtle chemical tests.  Information about which is found at any given locality is the best bet.  Fluorapophyllite is probably the more common of the two.
Cleavage Hardness Color Luster Name System Habit SG Notes
Perfect in one direction (may have a good cleavage in another direction) 4½  to 5 parallel to the length of the crystal, 7 to 7½ across the crystal Blue most common, also Green, may be Grey, even Black, due to inclusions Vitreous to subvitreous KYANITE
Al2SiO5		 Triclinic Most often as bladed long-prismatic crystals, usually poorly formed and rarely terminated, may be in parallel groupings or randomly oriented in the matrix 3.56 to 3.76 Only common mineral with significant hardness difference in two directions.
Two  directions:
Perfect in one direction (prismatic), good in another direction (prismatic)		 3½ to 4 Colorless to White or Grey, may be tinted other colors Vitreous to sub-vitreous, silky when fibrous STRONTIANITE
(Aragonite Group)
SrCO3		 Orthorhombic Usually in granular or fibrous aggregates, may be columnar, crystals short prismatic to acicular, often pseudo-hexagonal in cross-section (Ca-rich) 3.76 Effervesces mildly in cold acids, or not at all.  Distinguished from cerussite by its notably lower specific gravity, lighter feel.  Also it is not as common as cerussite.
Two directions:
Perfect in one direction, imperfect in a second (both prismatic)		 4½ Bluish-grey to Greenish-Grey (triphylite), White to Greyish-white streak, Clove-brown to Yellowish-brown, Salmon (lithiophilite) Vitreous to sub-vitreous, may be dull in granular massive material TRIPHYLITE/
LITHIOPHILITE
LiFePO4  
LiMnPO4		 Orthorhombic Usually in cleavable crystalline masses, crystals rare and usually crude with uneven surfaces, stout prismatic 3.56 (triphylite), 3.34 (lithiophilite)  
Cleavage Hardness Color Luster Name System Habit SG Notes
Two directions: Perfect in one direction (prismatic), good in a second direction (cleavages rarely seen) 4½ to 5 Colorless to White, may be Pale-yellow, Pale-green, Sky-blue, Pale-brown Vitreous, pearly on some cleavage surfaces HEMIMORPHITE
Zn4Si2O7(OH)2.H2O		 Orthorhombic Usually in radiating clusters of acicular or somewhat flattened long prismatic crystals, may also be in thick botryoidal crusts of thick to almost fibrous radiating crystals 3.4 to 3.5 May resemble prehnite in its botryoidal form, but S.G. is higher
Two directions: Perfect in both directions (prismatic & pinacoidal) 4½ to 5 White, Pale-pink, Pale-tan, Pale-blue Vitreous to silky in fibrous material PECTOLITE
(Wollastonite Group)
NaCa2Si3O8(OH)		 Triclinic Usually in acicular sprays or radial fibrous aggregates 2.84 to 2.90 Partly decomposed in acid forming a gel
Two directions: Perfect in one direction (prismatic), good in a second (pinacoidal), may exhibit a poor to good third cleavage (rarely seen) 4½ to 5 White to Greyish-white, may also be Pale-green Vitreous to somewhat pearly in fibrous material WOLLASTONITE-1A
(Wollastonite Group)
CaSiO3		 Triclinic Usually in coarsely crystalline cleavage masses, more rarely fibrous 2.86 to 3.09 Most common of the wollastonite polymorphs. Found in contact metamorphism of siliceous limestones
Cleavage Hardness Color Luster Name System Habit SG Notes
Two directions: Perfect in two directions (prismatic & pinacoidal) 4½ to 5 Orange to Pinkish-orange to Rose Vitreous, pearly on cleavage surfaces SERANDITE
(Wollastonite Group)
Na(Mn,Ca)2Si3O8(OH)		 Triclinic Usually as slightly flattened prismatic crystals in parallel to sub-parallel groups 3.0 to 3.4 Rare
Two directions: Perfect in one direction, imperfect in a second direction (both prismatic) 5 to 5½ Yellowish-brown to Greenish-brown Vitreous to sub-vitreous, may be somewhat resinous or oily TITANITE  ("SPHENE")
CaTiSiO5		 Monoclinic Usually in crude blocky to stout prismatic crystals, wedge-shaped 3.48 to 3.60 Streak white to pale brown
Two directions: Perfect in both directions at nearly 90o to one another (prismatic) 5½ to 6½ Pink to Rose-red, Brownish-red, usually coated with black manganese oxides Vitreous to sub-vitreous, may be somewhat pearly on cleavage surfaces RHODONITE
(Mn,Fe,Mg,Ca)SiO3		 Triclinic Usually massive, granular, rarely as tabular crystals 3.55 to 3.76  
Two directions: Perfect in two directions 5½ to 6 Dark Greenish-black to Black Vitreous, splendant. BABINGTONITE
Ca2(Fe,Mn)FeSi5O14(OH)		 Triclinic Usually as equant to stout prismatic to tabular crystals, often crude 3.34 to 3.48 Pale greenish to brownish grey streak
Cleavage Hardness Color Luster Name System Habit SG Notes
Two directions: Perfect in both directions (prismatic and pinacoidal) 4 to 4½ Colorless to White, may be Pink to Orange-red Silky to vitreous DACHIARDITE-Ca
(Zeolite Group)
(Ca0.5,K,Na)4-5[Al4-5Si20-19O48] .~13H2O		 Monoclinic Usually fibrous to small bladed prismatic crystals in radiating aggregates or clusters 2.14 to 2.21 White streak; Rare.
Two directions: Distinct in one direction, indistinct in another (both prismatic) 4 to 4½ Colorless to White, may be Pink to Red, Yellow Vitreous PHILLIPSITE-Ca
(Zeolite Group)
(Ca0.5,K,Na,Ba0.5)4-7[Al4-7,Si12-9O32]·12H2O		 Monoclinic Usually as small twinned, pseudo-orthorhombic, prismatic crystals 2.2 White streak; Forms a series with harmotome.
Two directions: Good in one direction, fair in another (both prismatic), fair cleavage may not be seen 4½ to 5 Colorless to White or Greyish-white, may be tinted other colors Vitreous HARMOTOME
(Zeolite Group)
(Ba0.5,Ca0.5,K,Na)5[Al5Si11O32]·12H2O		 Monoclinic Usually as blocky crystals, but may be twinned, pseudo-orthorhombic, prismatic crystals 2.38 to 2.50 (increasing with Ba content) Streak white; Forms a series with phillipsite
Two directions:
Perfect in one direction (prismatic), poor in another, (pinacoidal), second may not be seen		 4½ to 5½ Colorless to White, Pale-pink, Pale-yellow to Pale-brown Vitreous, pearly on some cleavage surfaces BREWSTERITE-Sr/
BREWSTERITE-Ba
(Sr,Ba)2[Al4Si12O32].10H2O
(Ba,Sr)2[Al4Si12O32].10H2O		 Monoclinic & Triclinic Usually as small tabular crystals, may be blocky or prismatic as well 2.32 to 2.45 (increasing with Ba content) Brewsterite-Ba is the far more common of the two
Cleavage Hardness Color Luster Name System Habit SG Notes
Two directions: Perfect in both directions (both prismatic) 5 Colorless to White, may be Pink to Red, Yellowish or Green Silky when fibrous, vitreous when acicular MESOLITE
(Zeolite Group)
Na16Ca16[Al48Si72O240].64H2O		 Orthorhombic Usually in fibrous radiating aggregates or long slender needles in sprays, stellate clusters, or jackstraw clusters, may also be fibrous tufts 2.25 White streak;
Two directions:
Perfect in both directions (both prismatic)		 5 to 5½ Colorless to White, Pink to Red or Salmon, Green Vitreous, silky in fibrous material SCOLECITE
(Zeolite Group)
Ca[Al2Si3O10].3 H2O		 Monoclinic Usually as thin flattened prismatic needles in stellate to radiating clusters, may also be in fibrous radiating aggregates 2.24 to 2.31 Rare.
Two directions:
Perfect in one direction (prismatic), good to distinct in a second direction (actually a parting, but distinct – prismatic)		 5 to 5½ Colorless to White, Pale-pink to Pale-red, may be other colors Vitreous, silky in more fibrous aggregates, more rarely greasy or dull NATROLITE
(Zeolite Group)
Na2[Al2Si3O10].2H2O		 Orthorhombic Usually as long slender needles or prismatic crystals (nearly square cross-section, pseudo-tetragonal) in radial aggregates or stellate or jackstraw clusters 2.20 to 2.27 White streak; partially decomposed by acid, producing a white gel.
Two directions:
Perfect in one direction, good in another (both prismatic), may not be seen		 5 to 5½ Colorless to White, may be tinted other colors, white streak Vitreous to pearly THOMSONITE
(Zeolite Group)
Ca2Na[Al5Si5O20]. 6H2O		 Orthorhombic Usually in granular masses, crystals vary from thin rectangular blades to blocky prismatic 2.25 to 2.44 Partially decomposed by acid, producing a white gel.
Two directions at ~56o and ~124o : prismatic – Amphibole Group; Good to perfect in both directions 5 to 6 Grey to Lavender-blue or Pale-blue Vitreous, silky in asbestiform varieties GLAUCOPHANE/ 
FERROGLAUCOPHANE
Na2(Mg3Al2)Si8O22(OH)2  
Na2(Fe3Al2) Si8O22(OH)2		 Monoclinic Usually in lath-like crystal aggregates, striated along their length, and in fibrous ("asbestiform") aggregates ("crocidolite") 3.02 to 3.42 (increasing with Fe content) Pale-grey to bluish-grey streak;  glaucophane usually light-grey to lavender-blue; ferroglaucophane usually darker. The glaucophanes and riebeckites are impossible to tell apart without subtle chemical or optical tests.
Cleavage Hardness Color Luster Name System Habit SG Notes
Two directions at ~56o and ~124o : prismatic – Amphibole Group; Good to perfect in both directions 5 to 6 Light-blue to Blue-black Vitreous, silky in asbestiform varieties MAGNESIORIEBECKITE/
RIEBECKITE
Na2(Mg3Fe2)Si8O22(OH)2
Na2(Fe3Fe2)Si8O22(OH)2		 Monoclinic Usually in lath-like crystal aggregates, striated along their length, and in fibrous ("asbestiform") aggregates ("crocidolite") 3.02 to 3.42 (increasing with Fe content) Pale-grey to bluish-grey streak; magnesioriebeckite usually lighter blue, riebeckite usually darker; glaucophanes and riebeckites are impossible to tell apart without subtle chemical or optical tests.
Two directions at ~56o and ~124o : prismatic – Amphibole Group; Perfect in both directions 5 to 6 White to Light-Green to Dark-green Vitreous, silky in asbestiform varieties TREMOLITE/
ACTINOLITE
Ca2Mg5Si8O22(OH)2  
Ca2(Fe,Mg)5Si8O22(OH)2		 Monoclinic Usually in bladed crystal aggregates, may also be somewhat acicular, tremolite may be asbestiform ("byssolite") or in fibrous mats ("mountain leather", "mountain cork"). The massive fibrous aggregate form of either is known as the variety nephrite, and is one of the materials called 'Jade.' 2.89 to 3.44 (increasing with Fe content) Tremolite usually white to greyish-white or pale greenish-white, actinolite medium- to dark-green.
Two directions at ~56o and ~124o : prismatic – Amphibole Group; Good to perfect in both directions 5 to 6 Brown to Greenish-brown to Green or Greyish-green Vitreous, silky in fibrous varieties CUMMINGTONITE/
GRÜNERITE
Mg7Si8O22(OH)2
Fe7Si8O22(OH)2		 Monoclinic Usually in bladed crystal aggregates or asbestiform, may be acicular 3.1 to 3.6 (increasing with Fe content) Cummingtonite usually green to grey-green, grünerite brown to greenish-brown.
Cleavage Habit Color Luster Name System Habit SG Notes
Two directions at ~56o and ~124o : prismatic – Amphibole Group; Perfect in one direction, imperfect in the second 5½ to 6 White to Grey or Pale-green to Clove-brown or Dark-brown Vitreous, silky in asbestiform varieties ANTHOPHYLLITE/
FERROANTHOPHYLLITE
Mg7Si8O22(OH)2   
Fe7Si8O22(OH)2		 Orthorhombic Usually columnar aggregates, may be radiating, or asbestiform 3.18 to 3.57 (increasing with Fe content) Anthophyllite usually lighter colors, ferroanthophyllite darker.
Two directions at ~56o and ~124o : prismatic – Amphibole Group; Perfect in one direction, imperfect in the other 5½ to 6 Pale Greenish-grey to Greenish-brown and Brown Vitreous, silky when fibrous GEDRITE/
FERROGEDRITE
Mg5Al2[Si6Al2O22](OH)2  
Fe5Al2[Si6Al2O22] (OH)2		 Orthorhombic Usually in lamellar to fibrous aggregates 3.18 to 3.57 (increasing with Fe content) Gedrite usually paler shades, ferrogedrite darker.
Two directions at ~56o and ~124o : prismatic – Amphibole Group; Perfect in both directions 5 to 6 Black to Greenish-black or Dark-green Vitreous MAGNESIOHORNBLENDE/
FERROHORNBLENDE
Ca2[Mg4(Al,Fe)]Si7AlO22(OH)2  
Ca2[Fe4(Al,Fe)]Si7AlO22(OH)2		 Monoclinic Usually in coarsely crystalline cleavable masses, also in prismatic to acicular crystal aggregates with the crystals often displaying a crudely pseudo-hexagonal cross section, otherwise rectangular to nearly square, not asbestiform 3.02 to 3.45 (increasing with Fe content) May give grey-green streak;  magnesiohornblende usually paler than ferrohornblende
Cleavage Hardness Color Luster Name System Habit SG Notes
Two directions at ~56o and ~124o : prismatic – Amphibole Group; Perfect in both directions 5 to 6 Pale-green to Dark-green, Greyish-brown to Brown, Yellow-brown to Reddish-brown or Rose-red Vitreous, silky in asbestiform varieties RICHTERITE/
FERRORICHTERITE
Na(Ca,Na)Mg5Si8O22(OH)2
Na(Ca,Na)Fe5Si8O22(OH)2		 Monoclinic Usually in cleavable prismatic crystal aggregates or stout flattened prismatic crystals, also asbestiform 2.97 to 3.45 (increasing with Fe content) Color darkens with increasing Fe content (ie: ferrorichterite).
Two directions at nearly 90o: prismatic – Pyroxene Group; Good to perfect in both directions 5 to 6 Pale to Medium-green, Pale-yellow to Light Yellowish-brown, Pale-bronze ("bronzite") Vitreous to sub-vitreous, may be sub-metallic in the "bronzite" and "hypersthene" varieties ENSTATITE/
CLINOENSTATITE
Mg2Si2O6		 Orthorhombic & Monoclinic Usually granular in rocks, rarely as short-prismatic crystals 3.21 to 3.60 Enstatite-ferrosilite and clinoenstatite-clinoferrosilite form solid solution series.  They are very difficult to tell apart.  "Bronzite" and "hypersthene" are varietal names for intermediate members of the series.
Cleavage Hardness Color Luster Name System Habit SG Notes
Two directions at nearly 90o: prismatic – Pyroxene Group; Good in both directions 5 to 6 Greenish-brown or Brown to nearly Black Vitreous to sub-vitreous, may be dull, may be pearly to sub-metallic on cleavage surfaces FERROSILITE/
CLINOFERROSILITE
(Fe,Mg)2Si2O6		 Orthorhombic & Monoclinic Usually granular in rocks, prismatic crystals rare 3.6 to 4.0 Streak pale grey to pale brown; Enstatite-ferrosilite and clinoenstatite - clinoferrosilite form solid solution series.  They are very difficult to tell apart.  "Bronzite" and "hypersthene" are varietal names for intermediate members of the series.
Two directions at nearly 90o: prismatic – Pyroxene Group; Good to perfect in both directions 5½ to 6 Pale- to Dark-green, may be White or Greenish-white to Greyish-white Vitreous to sub-vitreous, may be dull DIOPSIDE
CaMgSi2O6		 Monoclinic Usually as equant to stout prismatic crystals, slender prismatic less common, more rarely tabular, also massive and granular 3.22 to 3.45 White to pale-green streak; may exhibit chatoyancy and 4-ray asterism when cut and polished with the correct orientation. Diopside and hedenbergite form a solid solution series.  They can be impossible to distinguish visually.  S.G. usually tells them apart, though when of intermediate composition this may not do the trick.
Two directions at nearly 90o: prismatic – Pyroxene Group; Good in both directions 5½ to 6 Pale- to Dark-green, Brownish-green to Brownish- or Greenish-black Vitreous to sub-vitreous, may be dull HEDENBERGITE
CaFe Si2O6		 Monoclinic Usually as massive, granular, and as fracture fillings in rock, crystals equant to stout prismatic, slender prismatic less common, more rarely tabular 3.45 to 3.56 Pale green to tan streak;  may exhibit chatoyancy and 4-ray asterism when cut and polished with the correct orientation. Diopside and hedenbergite form a solid solution series.  They can be impossible to distinguish visually.  S.G. usually tells them apart, though when of intermediate composition this may not do the trick.
Cleavage Hardness Color Luster Name System Habit SG Notes
Two directions at nearly 90o: prismatic – Pyroxene Group; Good in both directions 5½ to 6 Greenish-black to Black, Light- to Dark-brown Vitreous to sub-vitreous, may be dull AUGITE
(Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6		 Monoclinic Usually granular in rocks, also as somewhat flattened short-prismatic crystals 3.19 to 3.56 Pale brown to greenish grey streak
Two directions at nearly 90o: prismatic – Pyroxene Group; Good to perfect in both directions 5½ to 6 Dark-green or Reddish-brown to Black Vitreous to sub-vitreous, may be dull AEGIRINE (ACMITE)
NaFeSi2O6		 Monoclinic Usually as slender prismatic or acicular crystals, either in clusters in cavities or as acicular aggregates in matrix 3.50 to 3.60 Pale tan to yellow green to pale green streak
Cleavage Hardness Color Luster Name System Habit SG Notes
Three directions: rhombohedral – Trigonal Carbonates: Perfect in all three directions 3, may be 2 across the top surface of prismatic crystals with a flat termination Usually Clear or White to Tan or Grey, but may be tinted many colors Vitreous to sub-vitreous luster, may be waxy or dull on weathered crystals, pearly on cleavage surfaces CALCITE
CaCO3		 Trigonal May be in cleavable masses producing rhombs, granular masses (limestone and marble), scalenohedral ("dogtooth") crystals, rhombohedral crystals, flattened rhombohedral ("nailhead") crystals, or a wide variety of related shapes (there are over 800 crystals forms known for this species to date…) 2.71 Clear rhombs show a doubled image of print viewed through them, , effervesces in cold, dilute acid – even in vinegar or Coke to a small degree. The many varied habits of calcite crystals make this one of the species that can be tough to identify by crystal form alone.  Few people, if any, are familiar with all the forms it takes.
Three directions: rhombohedral – Trigonal Carbonates: Perfect in all three directions 3½ to 4½ White to Grey, may be tinted Yellowish to Brownish Vitreous to sub-vitreous, may be pearly on cleavage surfaces MAGNESITE
(Calcite Group)
MgCO3		 Trigonal Usually massive, granular, crystals may be rhombohedral or prismatic but are rare 3.0 White streak;  only slightly soluble in cold acids.  No where near as common as calcite or dolomite.
Three  directions: rhombohedral – Trigonal Carbonates: Perfect in all three directions 3½ to 4 White to Tan or Pink, Grey, Greenish, tends towards Brown with increasing Fe, Red with Mn Usually vitreous to sub-vitreous, but may be pearly DOLOMITE
CaMg(CO3)2		 Trigonal Usually as massive, granular, or in curved rhombohedral crystal clusters "fingernail" shape, druzes may have a characteristic "saddleback" arrangement 2.85 Streak same color as sample, but pale; powder effervesces in cold acid, though not as vigorously as calcite, may be fluorescent. The Dolomite Group minerals are best told apart – and from calcite – by their S.G. when color and habit coincides.
Cleavage Hardness Color Luster Name System Habit SG Notes
Three  directions: rhombohedral – Trigonal Carbonates:  Perfect in all three directions 3½ to 4 White to Tan or Brown Usually vitreous to subvitreous, but may be pearly ANKERITE
(Dolomite Group)
Ca(Fe,Mg,Mn)(CO3)2		 Trigonal Usually  massive, granular, or as rhombohedral crystals (similar to dolomite) 2.87 White streak;  powder effervesces in cold acids, though not as vigorously as calcite.  Not as common as either calcite or dolomite. The Dolomite Group minerals are best told apart – and from calcite – by their S.G. when color and habit coincides.
Three  directions: rhombohedral – Trigonal Carbonates: Perfect in all three directions 3½ to 4 White to Pale-rose Vitreous to sub-vitreous, but may be pearly KUTNOHORITE
(Dolomite Group)
Ca(Mn,Mg,Fe) (CO3)2		 Trigonal Usually  massive crystalline cleavable into rhombs, more rarely as rhombohedral crystals 3.12 White streak;  powder effervesces in cold acids, though not as vigorously as calcite.  Rare. The Dolomite Group minerals are best told apart – and from calcite – by their S.G. when color and habit coincides.
Three  directions: rhombohedral – Trigonal Carbonates:  Perfect in all three directions 3½ to 4 Pink to Red (purer), in various shades, also more rarely Yellow-grey or Tan to Brown Vitreous to sub-vitreous, may be pearly on cleavage surfaces RHODOCHROSITE
(Calcite Group)
MnCO3		 Trigonal Usually in coarsely crystalline cleavable masses, crystals rhombohedral, may also be botryoidal and globular with concentric banding, and stalactic 3.5 to 3.7(pure) White streak; only slightly soluble in cold acids.  Uncommon.
Cleavage Hardness Color Luster Name System Habit SG Notes
Three  directions: rhombohedral – Trigonal Carbonates: Perfect in all three directions 4 to 4½ Greyish-white to Dark-grey, Greenish- or Brownish-white, may be Green to Apple-green, Blue to Blue-green, Yellow, Pink or Brown Vitreous to sub-vitreous, may look somewhat porcelain-like SMITHSONITE
(Calcite Group)
ZnCO3		 Trigonal Usually in botryoidal, reniform, and stalactic masses, rhombohedral crystals rare and usually crude with somewhat curved and rough surfaces, druzy 4.2 (pure) White streak; soluble in cold acids, though not with the vigorous effervescence of calcite.
Three  directions: rhombohedral – Trigonal Carbonates:  Perfect in all three directions 3½ to 4 Dark-brown to Tan to Cream, may be Blackish-brown due to weathering Vitreous to sub-vitreous, may be oily to resinous on weathered, oxidized surfaces SIDERITE
(Calcite Group)
FeCO3		 Trigonal Usually in cleavable coarsely crystalline masses, though not cleavable into rhombs, crystals rhombohedral, more rarely tabular,  very rarely prismatic 3.8 to 4.0 White streak;  somewhat soluble in cold acids, but with little or no effervescence
Three  directions: Perfect to distinct in all three directions, rhombohedral 3 to 5 Colorless to White, may be tinted various colors Vitreous to sub-vitreous CHABAZITE
(Zeolite Group)
(Ca0.5,K,Na)4[Al4Si8O22].12H2O		 Triclinic, pseudo-trigonal Usually as distorted cubes or pseudo-rhombohedral crystals (actually composed of six triclinic twins), rarely prismatic or tabular, then somewhat lens- or bean-shaped ("phacolitic") 1.97 to 2.20 Streak white;  partially dissolved in cold acids producing a gel, may be fluorescent.
Cleavage Hardness Color Luster Name System Habit SG Notes
Three  directions: Perfect to distinct in all three directions, rhombohedral 4 to 4½ Colorless to White, may be tinted various colors Vitreous to subvitreous LEVYNE
(Zeolite Group)
(Ca0.5,Na,K)6[Al6Si12O36].~17H2O		 Trigonal Usually as small to tiny platy hexagonal crystals 2.09 to 2.16 Streak white;  Rare.
Three  directions: Perfect in two directions, imperfect in a third, all prismatic 3 to 4 White, may be  tinted other colors Vitreous, pearly on cleavage surface, chalky when dehydrated LAUMONTITE
(Zeolite Group)
Ca4[Al8Si16O48].18H2O		 Monoclinic Usually as simple prismatic crystals with a square cross section, more rarely as equant crystals 2.20 to 2.41 White streak;  crystals may have chalky white coatings due to dehydration, may be fluorescent.  Rare.
Three  directions: One direction perfect, one imperfect, both prismatic, one good, basal 3 to 3½ Colorless to White, usually tinted other colors Vitreous to sub-vitreous, may be pearly on cleavage surfaces ANHYDRITE
CaSO4		 Orthorhombic Usually in coarsely crystalline masses showing pseudo-cubic cleavage, or granular or fibrous, crystals uncommon and usually equant or thick tabular 2.98 White streak; dissolves in cold acids without effervescence
Cleavage Hardness Color Luster Name System Habit SG Notes
Three  directions: Perfect in two directions, basal and prismatic, imperfect in a third, prismatic (rhombic overall) 3 to 3½ Colorless to White or Greyish-white, may be tinted other colors, streak white Vitreous, pearly on basal cleavage surfaces BARITE
BaSO4		 Orthorhombic Usually in clusters or aggregates of platy to tabular crystals 4.5 Heavy for its size. The three members of the Barite Group are most easily told apart by their S.G.s.  Anglesite is noticeably heavier than the other two, barite may feel heavier than celestite.
Three  directions: Perfect in one direction, basal, good in a second and fair to poor in a third, both prismatic (rhombic overall) 3 to 3½ White to Greyish-white, Blue, may be tinted other colors, streak white Vitreous, pearly on basal cleavage surfaces, CELESTITE (Celestine)
(Barite Group)
SrSO4		 Orthorhombic Usually in clusters or aggregates of platy to tabular crystals 3.95 to 3.97 Somewhat heavy for its size.  The three members of the Barite Group are most easily told apart by their S.G.s.  Anglesite is noticeably heavier than the other two, barite may feel heavier than celestite.
Three  directions: One distinct (prismatic), second direction good  (basal), and fair to poor in a third, (prismatic); rhombic overall – may be difficult to see all three 2½ to 3 Colorless to White or Greyish-white to Greyish-brown Adamantine to sub-adamantine, may be vitreous to resinous on some surfaces ANGLESITE
(Barite Group)
PbSO4		 Orthorhombic Usually in crystalline masses, crystals usually small and tabular, rarely prismatic 6.2 to 6.4 Streak white; very heavy.   Massive material may be difficult to distinguish from cerussite if cleavages can't be seen.  The three members of the Barite Group are most easily told apart by their S.G.s.  Anglesite is noticeably heavier than the other two, barite may feel heavier than celestite.
Cleavage Hardness Color Luster Name System Habit SG Notes
Three directions: perfect in two directions, prismatic, good to imperfect in a third, basal 3 to 3½ Colorless to White or Greyish-white, may be tinted other colors Vitreous and/or pearly. ANHYDRITE
CaSO4		 Orthorhombic Usually in coarsely crystalline masses exhibiting pseudo-cubic cleavage, or in granular masses with no apparent cleavage, crystals rare and usually equant or thick tabular 2.9 to 2.98 White streak;
Four  directions: Perfect in all four directions, octahedral 4 Colorless, Green, Purple, Blue, Yellow, Pink Vitreous FLUORITE
CaF2		 Isometric Usually in cubic crystals or coarsely crystalline masses exhibiting octahedral cleavage, crystals may also be octahedral 3.18 Streak white;  often fluorescent.  The term fluorescent is derived from this mineral's name.
Four  directions: Imperfect to distinct in two directions, good in two directions, all prismatic 5 to 6 White to Grey, Yellowish, Brownish, Orange, Purple Vitreous to subvitreous, may be dull also MARIALITE/
MEIONITE
(Scapolite series)
3NaAlSi3O8.NaCl  
3CaAl2Si2O8.CaCO3		 Tetragonal Usually massive, either columnar or fibrous, with columnar masses exhibiting cleavage surfaces, also as short to medium prismatic crystals with bipyramidal terminations, usually somewhat crude 2.55 to 2.72 May fluoresce yellow. It is almost impossible to tell the end members of this complex series apart without subtle chemical or optical tests.  Intermediate member, wernerite, is probably the most common chemical form found – though it is not recognized as a species in spite of evidence that it should be. It is probably best to label samples of these materials simply as scapolite, unless specific locality information dictates otherwise
Cleavage Hardness Color Luster Name System Habit SG Notes
Six directions: Perfect in all six directions, dodecahedral, but difficult to produce in some of them 3½ to 4 Brown to Black, Yellow-brown to Greenish-yellow-brown, may also be Red ("Ruby Jack") in small crystals Resinous, but may be oily or sub-metallic on cleavage surfaces and adamantine in small crystals SPHALERITE
(Zn,Fe)S		 Isometric Usually in coarsely crystalline cleavable masses exhibiting seemingly chaotic cleavage surfaces, and as small tetrahedral (wedge-shaped) or dodecahedral (soccer ball-shaped) crystals, larger crystals tend to be somewhat crude and rough surfaced aggregates 3.9 to 4.1 Brown to yellow streak
Six  directions:  Poor to distinct in all six directions, dodecahedral, may not be seen 5½ to 6 Medium-blue to Violet-blue, Greyish-white to White, more rarely Greenish- or Yellowish-white Vitreous to subvitreous, may be somewhat dull in massive material SODALITE
Na8Al6Si6O24Cl2		 Isometric Usually as granular masses or grains in matrix, sometimes crudely cleavable, crystals rare, usually dodecahedral to cubo-dodecahedral, rarely octahedral 2.14 to 2.30 White to very pale blue streak; usually associated with nepheline – never with quartz.
Six  directions: Poor to distinct in all six directions, dodecahedral, may not be seen 5 to 5½ Deep-blue to Medium-blue or Violet-blue, may be Greenish-blue, Colorless Dull to vitreous LAZURITE
(Sodalite Group)
(Na,Ca)7-8(Al,Si)12(O,S)24[(SO4),Cl2,(OH)2]		 Isometric, Triclinic, and Monoclinic polytypes Usually as compact massive material or grains, crystals rare, usually well-formed dodecahedral to cubo-dodecahedral 2.38 to 2.45 Bright blue streak; usually found with pyrite.

Notes:
Single and double cleavage direction Zeolites can be difficult to tell apart. Hardness may help to distinguish the harder and softer species from one another, and crystal habit and form may help to tell some species apart. In general, habits and forms taken with hardnesses are the best indicators.

Amphiboles are a large and difficult group to tell apart. The best bet is location-specific knowledge.

Pyroxenes can be difficult to distinguish from one another.    Locality information is usually the best bet for determining what you have.

Table of Contents   Return to Step 11

Table IID-2: Nonmetallic Luster; Hardness greater than 3 but less than 5½, Cleavage not prominent: (Can not be scratched by a copper penny, can be scratched by a knife, streak white or none.)
Hardness Color Luster Name System Habit SG Notes
2½ to 3 Bright-yellow, Orange-yellow, Orange, Red, Grey, Green, White Sub-adamantine to vitreous, may be greasy WULFENITE
PbMoO4		 Tetragonal Usually as thin platy to thin tabular crystals, rarely pyramidal, more rarely prismatic 6.7 to 7.0  
2½ to 3 Orange-red to Ruby-red, Brownish-red to Brownish-yellow or Pale Straw-yellow Sub-vitreous to sub-resinous VANADINITE
(Apatite Group)
Pb5(VO4)3Cl		 Hexagonal Usually in barrel-shaped hexagonal crystals, long or short prismatic, may be acicular in clusters or mats ("endlichite"), and as hollow prisms – "hopper" crystals 6.88 Streak white, may be yellowish
2½ to 4, rarely 5 to 6 in dense massive material Apple-green to Yellow-green, Dark-green to Dark Grey-green, Greenish-black, White, often mottled Sub-vitreous to greasy ANTIGORITE/LIZARDITE/
AMESITE
(Serpentine Group)
(Fe,Mg)3(Si,Al)2O5(OH)4
Mg3(Si,Al)2O5(OH)4
Mg2Al(Si,Al)2O5(OH)4		 Monoclinic, Orthorhombic and Triclinic Usually as crystalline masses, often platy or columnar 2.4 to 2.79 White streak; feels greasy. These Serpentine minerals are almost impossible to tell apart, particularly in massive forms.  They may coexist at the same locality.  Specific locality information may be the best bet for the ID.
Hardness Color Luster Name System Habit SG Notes
3, but may be 2 across the top surface of prismatic crystals with a flat termination Usually Clear or White to Tan or Grey, but may be tinted many colors Vitreous to sub-vitreous CALCITE
CaCO3		 Trigonal May be in banded masses or stalactic ("flowstone"), granular masses (limestone and marble), or fibrous 2.71 White streak;  effervesces in cold, dilute acid – even in vinegar or Coke to a small degree. Cleavage is difficult to observe in some massive forms.
3 to 3½ Colorless to White or Greyish-white, may be tinted other colors Vitreous to sub-vitreous WITHERITE
(Aragonite Group)
BaCO3		 Orthorhombic, pseudo-hexagonal In coarse fibrous aggregates, may be radiating, and granular, more rarely as globular to botryoidal clusters 4.29 Often hazed, will effervesce in cold acid. Cleavage is difficult to observe in some massive forms.
3½ Bright-green to Yellow-green, Yellow to Orange-yellow, Brown, White, colorless Sub-vitreous to resinous PYROMORPHITE
(Apatite Group)
Pb5(PO4)3Cl		 Hexagonal Usually in barrel-shaped hexagonal crystals, may also be spindle-shaped, hollow – "hopper" crystals – and rarely tabular or pyramidal, crystals may exhibit concentric color or structural zones due to zoned variations in composition 7.04 White streak; difficult to distinguish from mimetite without tests for PO4 vs. AsO4.
Hardness Color Luster Name System Habit SG Notes
3½ to 4 Pale-yellow to Yellow-brown, Orange-yellow to Orange-red, White or Colorless Sub-vitreous to resinous MIMETITE
(Apatite Group)
Pb5(AsO4)3Cl		 Hexagonal Usually in simple barrel-shaped crystals, rarely tabular to acicular, may be botryoidal or globular 7.28 Streak white; Difficult to distinguish from pyromorphite  without tests for AsO4 vs. PO4.  Named for the fact that it closely mimics pyromorphite.
3½ to 4 Colorless to White or Grey, may be tinted other colors Vitreous to sub-vitreous or resinous ARAGONITE
CaCO3		 Orthorhombic In columnar, radiating or stellate aggregates, also stalactic 2.95 Often fluorescent, pale rose, yellow or bluish-white, effervesces in cold acids.  Distinguished from calcite by its greater hardness and higher S.G. Cleavage is difficult to observe in some massive forms.
3½ to 4 Colorless to White or Grey, may be tinted other colors Vitreous to sub-vitreous, silky when fibrous STRONTIANITE
(Aragonite Group)
SrCO3		 Orthorhombic In granular or fibrous aggregates, may be columnar, crystals short prismatic to acicular, often pseudo-hexagonal in cross-section (Ca-rich) 3.76 Effervesces mildly in cold acids
3½ to 4½ White to Grey, may be tinted Yellowish to Brownish Vitreous to sub-vitreous, may be pearly on cleavage surfaces MAGNESITE
(Calcite Group)
MgCO3		 Trigonal Usually massive, granular, crystals may be rhombohedral or prismatic but are rare 3.0 White streak;  only slightly soluble in cold acids.
Hardness Color Luster Name System Habit SG Notes
3½ to 4 White to Greyish-white, Reddish to Reddish-brown, Yellowish Dull to sub-vitreous ALUNITE
KAl3(SO4)2(OH)6		 Trigonal Usually massive, granular to dense, associated in rock with quartz, kaolinite, etc 2.6 to 2.9 Large deposits formed by action of sulfate bearing hydrothermal fluids. Small deposits formed by sulfates formed by the weathering of pyrite.
3½ to 4 Yellowish-green, Green to Yellow, Yellow-brown, Brown, more rarely Blue, White, Colorless Vitreous to pearly or resinous WAVELLITE
Al3(PO4)2(OH,F)3.5H2O		 Orthorhombic Usually stellate or hemispherical radial fibers or acicular crystals 2.36 White streak;  dissolves in cold acids with no effervescence.
4 to 4½ Greyish-white to Dark-grey, Greenish- or Brownish-white, may be Green to Apple-green, Blue to Blue-green, Yellow, Pink or Brown Vitreous to sub-vitreous, may look somewhat porcelain-like SMITHSONITE
(Calcite Group)
ZnCO3		 Trigonal Usually in botryoidal, reniform, and stalactic masses, rhombohedral crystals rare and usually crude with somewhat curved and rough surfaces, druzy 4.2 (pure) White streak;  soluble in cold acids, though not with the vigorous effervescence of calcite
4½ to 5 Colorless to White, may be Pale-yellow, Pale-green, Sky-blue, Pale-brown Vitreous, pearly on some cleavage surfaces HEMIMORPHITE
Zn4Si2O7(OH)2.H2O		 Orthorhombic Usually in radiating clusters of acicular or somewhat flattened long prismatic crystals, may also be in thick botryoidal crusts of thick to almost fibrous radiating crystals 3.4 to 3.5 May resemble prehnite in its botryoidal form, but S.G. is higher.
4½ to 5 White to Colorless, Pale-yellow, Pale-green, Pale-orange Vitreous to adamantine SCHEELITE
CaWO4		 Tetragonal Usually as grains or flakes, crystals rare and usually either platy to thin tabular or short-prismatic bipyramids 6.1 White streak;  fluoresces intense blue-white, more rarely yellowish white.
Hardness Color Luster Name System Habit SG Notes
4½ to 5 White, Pale-pink, Pale-tan, Pale-blue Vitreous to silky in fibrous material PECTOLITE
(Wollastonite Group)
NaCa2Si3O8(OH)		 Triclinic Usually in acicular sprays or radial fibrous aggregates 2.84 to 2.90 Partly decomposed in acid forming a gel
5 to 5½ Colorless to White, Pale-pink, may be Grey or other colors Usually vitreous to silky in finer acicular aggregates, but may be dull or even greasy NATROLITE
(Zeolite Group)
Na2[Al2Si3O10].2H2O		 Orthorhombic Usually as long slender needles in stellate clusters or radial aggregates, may also be in jackstraw clusters 2.20 to 2.27 White streak;  dissolves in cold acids
5 to 5½ Colorless to White, may be Yellow, Pink, or other colors Vitreous ANALCIME
(Zeolite Group)
Na[AlSi2O6].H2O		 Polymorphous (Iso., Tet., Orth., Mon., Tric., Trig.) Usually in cubic or trapezohedral crystals or fine-grained masses, more rarely in other crystal forms 2.22 to 2.63 Dissolves in cold acids
5 to5½ White, usually tinted Pale-green, may be Pale-blue Vitreous to greasy DATOLITE
(Gadolinite Group)
Ca2B2Si2O8(OH)2		 Monoclinic May be either platy to short prismatic or blocky crystals, more rarely as spherical aggregates or massive, granular to compact 2.9 to 3.0 White streak;  may show an imperfect basal cleavage, may fluoresce
Hardness Color Luster Name System Habit SG Notes
5 to 6 White, Yellow, Red, Brown, Black Vitreous OPAL
SiO2.nH2O		 Amorphous Glassy massive material, as fracture fillings, coatings, "nodules," etc. 1.9 to 2.1 Distinguished from massive quartz by lower hardness and S.G.  Precious opal has an intense internal play of colors – the fire comes from the natural diffraction grating of ordered spheres of a diameter approximately the size of a wavelength of light; in fire opal the flashes are predominantly reds, yellows and oranges against a black background.  Common opal is "opalescent," but without the intense flashes of colors.
5 to 6 White to Grey, Yellowish, Brownish, Orange, Purple Vitreous to subvitreous, may be dull MARIALITE/
MEIONITE
(Scapolite series)
3NaAlSi3O8. NaCl 
3CaAl2Si2O8.CaCO3		 Tetragonal Usually massive, either columnar or fibrous, (columnar masses may exhibit prismatic cleavage surfaces), also as short to medium prismatic crystals with bipyramidal terminations, usually somewhat crude 2.55 to 2.72 May fluoresce yellow.  It is almost impossible to tell the end members of this series apart without subtle chemical or optical tests.  Intermediate member, wernerite, is probably the most common , though it is not recognized as a species.  It is  best to label samples of these materials simply as scapolite, unless specific locality information dictates otherwise.
Hardness Color Luster Name System Habit SG Notes
5 White to Colorless, Greens, Blues, Lavender, Yellows, Purples Vitreous to sub-vitreous, may be dull in massive material FLUORAPATITE
(Apatite Group)
Ca5(PO4)3F		 Hexagonal Variable, may be massive, compact or granular, and may be in short- to long-prismatic crystals with a wide variety of habits, the hexagonal prism with pyramidal termination(s) being the most common, but may also be short-prismatic and even bipyramidal without the prism in between, also acicular 3.1 to 3.2 White streak;
Closely related members of the Group include chlorapatite, hydroxyl-apatite, carbonate-fluorapatite and carbonate-hydroxylapatite, which can be difficult to distinguish from fluorapatite – but they are rare
5 to 5½ Yellowish- or Reddish-brown to Brown, Pale-green to nearly White Resinous to waxy MONAZITE
(Ce,La,Y,Th)PO4		 Monoclinic Usually in crude blocky to tabular crystals, may be large, also as rounded grains 4.6 to 5.3, increasing with Th content Streak very pale brown;  may be radioactive.
Hardness Color Luster Name System Habit SG Notes
5 to 5½ Light-green to Yellow-green, Yellow-brown to Reddish-brown, Colorless Vitreous, occasionally resinous WILLEMITE
Zn2SiO4		 Trigonal Usually massively crystalline or granular, rarely in prismatic hexagonal crystals 4.05 to 4.20 Fluoresces bright green
5½ to 6 Medium-blue to Violet-blue, Greyish-white to White, more rarely Greenish- or Yellowish-white Vitreous to subvitreous SODALITE
Na8Al6Si6O24Cl2		 Isometric Usually as granular masses or grains in matrix, sometimes crudely cleavable, crystals rare, usually dodecahedral to cubo-dodecahedral, rarely octahedral 2.14 to 2.30 White to very pale blue streak;   may be somewhat dull in massive material, usually associated with nepheline – never with quartz.
5 to 5½ Deep-blue to Medium-blue or Violet-blue, may be Greenish-blue, Colorless   LAZURITE
(Sodalite Group)
(Na,Ca)7-8(Al,Si)12(O,S)24[(SO4),Cl2,(OH)2]		 Isometric, Triclinic, and Monoclinic polytypes Usually as compact massive material or grains, crystals rare, usually well-formed dodecahedral to cubo-dodecahedral 2.38 to 2.45 Luster dull to vitreous, usually found with pyrite

Table of Contents   Return to Step 11

Table IIIA-1: Hardness greater than 5½ but less than 7; Cleavage prominent (Can not be scratched by a knife, can be scratched by quartz.)
Cleavage Hardness Color Luster Name System Habit SG Notes
Perfect in one direction (prismatic) 4 to 5 parallel to cleavage and crystal faces, 6 to 7 across crystal and cleavage faces Blue, Green, Grey, White, very rarely Black Vitreous to sub-vitreous KYANITE
Al2SiO5		 Triclinic Usually in bladed aggregates, parallel or radiating, may also be single flattened prismatic crystals 3.56 to 3.67 Only common mineral in which the hardness is so notably different along its length vs. across its width.
Perfect in one direction (prismatic) 5 to 6½ Light-brown to Black Resinous or pitchy/ submetallic ALLANITE-(Ce)
(Epidote Group)
(Ce,Ca,Y)2(Al,Fe,Fe)3(SiO4)3(OH)		 Monoclinic Usually in coarsely crystalline massive form, crystals tabular, prismatic to acicular (may be metamict), may also be finer grained with no apparent cleavage 3.4 to 4.2 May give a light brown streak; Allanite-(La) and Allanite-(Y) are closely related species, but extremely rare. Most of the Epidote group minerals may exhibit a second, poor, cleavage, but it is usually not seen.  See also clinozoisite below.
Perfect in one direction (prismatic) 6½ to 7 Green to Yellow-green, Yellow, Grey, Brownish-green, Greenish-black, Black Vitreous to sub-vitreous , dull in weathered crystals and massive materials EPIDOTE
Ca2(Fe,Al)3(SiO4)3(OH)		 Monoclinic Usually in short to long prismatic crystals, may also be thick tabular or acicular; also massive, coarse to fine granular, rarely fibrous 3.38 to 3.49 Over 200 different forms are known; Commonest of the Epidote Group species. Most of the Epidote group minerals may exhibit a second, poor, cleavage, but it is usually not seen.  See also clinozoisite below.
Cleavage Hardness Color Luster Name System Habit SG Notes
Perfect in one direction (prismatic) 6 to 7 Grey, Green to Yellowish-green, Pinkish, Brown, Blue, Purple, Colorless Vitreous, may be pearly on cleavage surfaces ZOISITE
(Epidote Group)
Ca2Al3(SiO4)3(OH)		 Orthorhombic Usually in aggregates of crude parallel crystals with vertical striations on the faces, more rarely as well-formed prismatic crystals in clusters or singly 3.15 to 3.36 The blue gem variety "tanzanite" and pink gem variety "thulite" are rare. Most of the Epidote group minerals may exhibit a second, poor, cleavage, but it is usually not seen.  See also clinozoisite below.
Perfect in one direction (prismatic) 6½ to 7 Colorless to White, Grey, Pale-brown to Pale-yellow, more rarely Pale-blue to Pale-green Vitreous to sub-vitreous, silky in fibrous material, may be dull on weathered surfaces SILLIMANITE
Al2SiO5		 Orthorhombic Usually as crude prismatic crystals with a nearly square cross-section,  may be in columnar to fibrous aggregates ("fibrolite") 3.23 to 3.27 Surfaces often rough and altering to muscovite, restricted to high-temperature and pressure metamorphic environments
Cleavage Hardness Color Luster Name System Habit SG Notes
Two directions at or nearly 90o. Perfect in one direction (prismatic) 6½ to 7 White to Greyish-white, Colorless, Pinkish-white to Pale-lavender, more rarely Greenish to Yellowish, Brown, Rose-red to Dark-red Vitreous to sub-adamantine, "brilliant" DIASPORE
AlO(OH)		 Orthorhombic Usually in thin platy crystalline aggregates, crystals thin, platy, may be prismatic or acicular, rarely tabular 3.35 to 3.45 Very brittle.  Often mistaken for milky to greyish quartz.
Perfect in two directions (prismatic) 6 Brown to Greenish-brown, Colorless, Black Vitreous PIGEONITE
(Pyroxene Group)
(Mg,Fe,Ca)(Mg,Fe)Si2O6		 Monoclinic Usually as matrix-bound crystalline grains in cooled lavas 3.17 to 3.46 Often inverts to augite after cooling.  Relatively rare compared to other Pyroxenes
Perfect in two directions (prismatic) 6½ to 7 Grey to White, Colorless, Tan, Yellow, Pale-green to Bright-green ("hiddenite"), Pink to Lilac to Violet ("kunzite") Vitreous to sub-vitreous SPODUMENE
(Pyroxene Group)
LiAlSi2O6		 Monoclinic Crystals are usually prismatic with a diamond shaped cross-section; but matrix-frozen crystals - the most commonly seen - tend to show only two adjacent faces, the other two not developed;  then they look like a triangular prism with two developed faces and a rough base to the 'triangle' - only half of the complete prism developed. 3.03 to 3.23 Crystals often very large, to 14 meters or more, crystals faces usually have a wood-grain look to them, gem quality material often with acid-etched crystal faces, heavily vertically striated.
Perfect in two directions (prismatic),
often not apparent		 6 to 7 Dark-green to Medium-green to (more rarely) Pale-green, White to Grey or Bluish-grey, Lavender to Violet Vitreous to sub-vitreous, may be dull in granular material JADEITE
(Pyroxene Group)
Na(Al,Fe)Si2O6		 Monoclinic Usually in compact massive material, granular or short fibrous, with cleavage not apparent 3.24 to 3.43 Massive material often a mix of jadeite and diopside, crystals extremely rare. [See also the softer Pyroxene Group minerals, IID, two cleavage directions, The hardness of many of them spans the 5 to 6 range, so they may key out to this point.]
Cleavage Hardness Color Luster Name System Habit SG Notes
Perfect in one direction, distinct in the second (prismatic) 6 White to Colorless, Cream to Tan  Vitreous to sub-vitreous, may be pearly on cleavage SANIDINE
(Feldspar Group)
K(Al,Si)4O8		 Monoclinic Usually as tabular crystals (phenocrysts) in rhyolites and other felsic extrusive volcanic rocks and as spherulites in obsidian 2.56 to 2.62 Association with rhyolites and other extrusive igneous rocks is distinctive. Carlsbad twins - mirrored inter-penetration twins exhibiting two terminations at each end - are common.
Perfect in one direction, good in the second (prismatic) 6 to 6½ White to Colorless, Cream to Tan and Pale-yellow, Salmon-pink to Red, Green to Blue-green ("Amazonite") Vitreous to sub-vitreous, may exhibit opalescence ("adularia") MICROCLINE
(Feldspar Group)
KAlSi3O8		 Triclinic Usually as coarsely crystalline rock-forming masses or macro-crystals in the 1 meter to 10s of meters range, smaller crystals usually short-prismatic to blocky, often twinned 2.54 to 2.57 Microcline and orthoclase are actually polytypes of a single species, and are extremely difficult to tell apart without subtle crystallographic observations.  The best bet for these is site-specific knowledge about what is found there.
Perfect in one direction, imperfect in the second (prismatic) 6  to 6½ White to Colorless, Cream to Tan to Pale-yellow, Pink to Brownish-red Vitreous to sub-vitreous, may be dull in granular masses, may exhibit pale blue to white opalescence ("moonstone") ORTHOCLASE
(Feldspar Group)
KAlSi3O8		 Monoclinic Usually massive, coarsely crystalline to granular, crystals usually short prismatic, blocky, often twinned 2.55 to 2.63 Microcline and orthoclase are actually polytypes of a single species, and are extremely difficult to tell apart without subtle crystallographic observations.  The best bet for these is site-specific knowledge about what is found there.
Cleavage Hardness Color Luster Name System Habit SG Notes
Perfect in one direction, good in the second (prismatic) 6 to 6½ White to Light-grey and Colorless, in albite, may be tinged Blue or Green, darkening to Dark-grey to Black in anorthite, intermediate members Medium to Darker greys (rarer than end members) Vitreous, labradorite exhibits opalescence/ "labradorescence" ALBITE/
ANORTHITE
(Plagioclase Series)
NaAlSi3O8  
CaAl2Si2O8		 Triclinic Usually massive, coarsely crystalline, platy lamellar habit in albite ("cleavlandite"), more randomly oriented and smaller grains in anorthite end of the series, including labradorite, crystals usually tabular and usually twinned in albite, usually short-prismatic and twinned in anorthite, euhedral crystals rare except for albite 2.60 to 2.65 (albite)
2.63 to 2.66 (oligoclase)
2.66 to 2.68 (andesine)
2.68 to 2.74 (labradorite)
2.72 to 2.75 (bytownite)
2.74 to 2.76 (anorthite)		 S.G. increases with replacement of Na by Ca and addition of Al, members to the albite end of the series most easily distinguished from other feldspars by fine, closely-spaced striations on the {001} cleavage plane, members towards the anorthite end of the series by their dark color and randomly oriented grains in massive materials.  Intermediate members usually difficult to distinguish from one another.
Perfect in one direction (prismatic), good in the other (pinacoidal) 5½ to 6½ Pink to Rose-red to Brownish-red, may also be Orangish-red in some weathered material Vitreous to sub-vitreous, may be dull in massive material RHODONITE
(Mn,Fe,Mg,Ca) SiO3		 Triclinic Usually massive, coarse to fine granular, crystals tabular to equant, rare 3.55 to 3.76 Often coated and/or veined with black Mn-oxides due to chemical weathering ("spider-web" veining).
Cleavage Hardness Color Luster Name System Habit SG Notes
Perfect in one direction (prismatic), imperfect in the other (pinacoidal) 5½ to 6 Black to Dark greenish-black Vitreous to splendant BABINGTONITE
(Rhodonite Group)
Ca2(Fe,Mn)FeSi5O14(OH)		 Triclinic Usually as equant to short-prismatic crystals 3.34 to 3.48 May give a greenish to brownish-grey streak; usually associated with zeolites in basalts ("traprock") more rarely in granitic rocks.  Rare.
Perfect in one direction, imperfect in the second direction (both prismatic) 5 to 5½ Yellowish-brown to Greenish-brown Vitreous to sub-vitreous, may be somewhat resinous or oily. TITANITE ("SPHENE")
CaTiSiO5		 Monoclinic Usually in crude blocky to stout prismatic crystals, wedge-shaped 3.48 to 3.60 Streak white to pale brown;
Perfect in two directions (prismatic and pinacoidal) 6½ Pale yellowish-grey to Yellowish-green, Colorless, Pale-rose to Red Vitreous to sub-vitreous CLINOZOISITE
(Epidote Group)
Ca2Al3(SiO4)3(OH)		 Monoclinic Usually as massive, granular to fibrous, crystals prismatic, often striated 3.21 to 3.38 Distinguished from other common Epidote group minerals by its second perfect cleavage.
Cleavage Hardness Color Luster Name System Habit SG Notes
Perfect in one direction (prismatic), imperfect in another (pinacoidal), distinct in a third (prismatic), and may have a fourth, good, direction (prismatic) 5½ to 6 White to Milky- or Cream-white, Grey, Yellowish to Tan or Beige, Salmon-pink, may also be Greenish or Bluish, Colorless Vitreous to greasy AMBLYGONITE/
MONTEBRASITE
LiAl(PO4)F 
LiAl(PO4)(OH)		 Triclinic Usually as crude equant to short-prismatic crystals, may be extremely large (meter scale), and as massive crystalline, coarse to fine granular 3.11 It is impossible to tell the two end members apart without subtle optical tests. Locality info may not help; eg. "amblygonite" specimens from Maine pegmatites have been shown to actually be montebrasite. It is probably best to label specimens as shown under Name unless there is proof positive of which end member you have

Note: Two cleavage directions at ~56o and ~124o = Amphibole Group.  A number of the Amphiboles have hardnesses in the 5 to 6 range, spanning previous sections and this one, and may key out to this point.  See IID-1.

Table of Contents   Return to Step 13

Table IIIA-2: Nonmetallic Luster; Hardness Greater Than 5½ and Less Than 7; Cleavage not prominent. (Can not be scratched by a knife blade, but can be scratched by quartz)
Hardness Color Luster Name System Habit SG Notes
5 to 5½ Colorless to White, usually tinted Pale-green, may be Pale-blue Vitreous to greasy DATOLITE
(Gadolinite Group)
Ca2B2Si2O8(OH)2		 Monoclinic May be either platy to short-prismatic or blocky crystals, more rarely as spherical aggregates or massive, granular to compact 2.9 to 3.0 White streak, may show an imperfect basal cleavage, may fluoresce.
5 to 6 White, Yellow, Red, Brown, Black Glassy OPAL
SiO2.nH2O		 Amorphous Massive, as fracture fillings, coatings, "nodules," etc. 1.9 to 2.1 Distinguished from massive quartz by lower hardness and S.G.; Precious opal has an intense play of colors – the fire comes from the natural diffraction grating of ordered spheres of a diameter approximately the size of a wavelength of light; in fire opal the flashes are predominantly reds, yellows and oranges against a black background. Common opal is "opalescent," but without the intense flashes of color.
5 to 5½ Azure-blue to Sky-blue, more rarely Bluish-white to Bluish-green Vitreous to sub-vitreous LAZULITE/
SCORZALITE
MgAl2(PO4)2 (OH)2
FeAl2(PO4)2(OH)2		 Monoclinic Usually as finely crystalline crusts or granular, crystals rare and usually millimeter size, acutely pyramidal, tabular 3.08 to 3.38 (increases with Fe content) White streak; Rare.
5 to 6 Sky-blue to Bluish-green to Apple-green, Green-grey Vitreous to sub-vitreous TURQUOISE
CuAl6(PO4)4(OH)8.4H2O		 Triclinic Usually massive in crusts and fracture fillings, dense to finely crystalline, crystals rare, short-prismatic 2.6 to 2.8 White to pale-green streak, may exhibit a perfect cleavage (pinacoidal), but rarely seen. Massive material may test softer due to granular/earthy texture
Hardness Color Luster Name System Habit SG Notes
5 to 6 White to Grey, Yellowish, Brownish, Orange, Purple   MARIALITE/
MEIONITE
(Scapolite series)
3NaAlSi3O8·NaCl  3CaAl2Si2O8·CaCO3		 Tetragonal Usually massive, either columnar or fibrous (columnar masses may exhibit prismatic cleavage surfaces), also as short to medium prismatic crystals with bipyramidal terminations, usually somewhat crude 2.55 to 2.72 May fluoresce yellow. It is almost impossible to tell the end members apart without subtle chemical or optical tests.  An intermediate member, wernerite, is probably the most common chemical form found – though it is not recognized as a species.  It is probably best to label samples of these materials simply as scapolite, unless specific locality information dictates otherwise.
5½ Light-green to Yellow-green, Yellow-brown to Reddish-brown, Colorless Vitreous, to resinous WILLEMITE
(Phenakite Group)
Zn2SiO4		 Trigonal Usually massively crystalline or granular, rarely in prismatic hexagonal crystals 4.05 to 4.20 Fluoresces bright green
5½ to 6 Greyish-white to White, Colorless Vitreous to sub-vitreous, may be dull LEUCITE
K(AlSi2O6)		 Tetragonal and Isometric Usually massive, granular, disseminated grains, crystals equant or blocky (soccer ball shaped), often multiply twinned 2.45 to 2.50 Restricted to mafic and ultramafic volcanic and hypabyssal rocks.
Hardness Color Luster Name System Habit SG Notes
5½ to 6 White, often tinted yellowish or greenish, Grey, Reddish-brown Vitreous to greasy NEPHELINE
(Na,K)AlSiO4		 Hexagonal Usually as crystalline grains or massively crystalline, crystals rare, hexagonal prisms with pinacoidal or pyramidal terminations 2.55 to 2.67 May exhibit a distinct prismatic cleavage in massively crystalline material, but rarely seen.
5½ to 6 Black to Light-brown Resinous or pitchy, may appear sub-metallic ALLANITE-(Ce)
(Epidote Group)
(Ce,Ca,Y)2(Al,Fe)3(SiO4)3(OH)		 Monoclinic Usually massive, may be platy, metamict, crystals tabular to prismatic to acicular 3.4 to 4.2 May give a light-brown streak, Allanite-(La) and allanite-(Y) are closely related species, but very rare.
5½ to 6 Brown, Yellowish-brown, Reddish-brown; Dark-brown to Iron-black; Metallic adamantine to submetallic BROOKITE
TiO2		 Orthorhombic Usually tabular, elongated and striated crystals, commonly pyramidal or pseudohexagonal 4.08 to 4.18 Found in alpine veins in gneiss and schist. Also found in contact metamorphic and hyrothermal veins
5½ to 6½ Colorless to White or Greyish-white, Pale-tan Vitreous EUCRYPTITE
(Phenakite Group)
LiAlSiO4		 Trigonal Usually coarsely crystalline, granular or compact,  crystals equant 2.66 Soluble in acid producing silica gel, fluoresces bright pink to red.
5 to 6½ Green or Chartreuse, Yellow to Yellow-green to Yellow-brown to Brown, Pink to Red, Black, White, Purple, Blue Vitreous to sub-vitreous VESUVIANITE
("Idocrase")
Ca10Mg2Al4(SiO4)5(Si2O7)2(OH)4		 Tetragonal Usually as stout prismatic crystals 3.32 to 3.43 Usually restricted to skarns, rodingites, and certain alkali syenites, and calc-silicate rocks.
6 to 6½ Pale-yellow, Brownish-red to Reddish- or Greenish-brown, Pale-orange Vitreous to greasy CHONDRODITE
(Humite Group)
(Mg,Fe)5(SiO4)2(F,OH)2		 Monoclinic Usually in equant crystalline grains, crystals equant, blocky 3.1 to 3.23 Soluble in acids producing silica gel, may fluoresce yellowish-white to yellow.
Hardness Color Luster Name System Habit SG Notes
6 to 6½ Yellow to Dark-orange, Reddish-orange Vitreous to sub-vitreous HUMITE
(Mg,Fe)7(SiO4)3(F,OH)2		 Orthorhombic Usually in equant crystalline grains, crystals extremely rare, also equant, blocky 3.20 to 3.32 Soluble in acids producing silica gel.  Relatively rare.
6 to 6½ Pale- to Medium-green, Pale-yellow, Tan to Pinkish-tan, Grey to White Vitreous to sub-vitreous, may be somewhat pearly on freshly broken exposures PREHNITE
Ca2Al2Si3O10(OH)2		 Orthorhombic Usually botryoidal to mammillary aggregates encrusting matrix, also stalactic and as radiating "bowtie" or "hourglass" aggregates, crystals extremely rare, short-prismatic to tabular 2.90 to 2.95 Slowly soluble in HCl producing silica gel. Often associated with Zeolites in traprock.
6 to 6½ Dark Reddish-brown to Black Usually sub-adamantine to adamantine, but may also be metallic RUTILE
TiO2		 Tetragonal Usually as prismatic to acicular crystals, often reticulated, may be vertically striated 4.18 to 5.25 Often as an inclusion in quartz
Hardness Color Luster Name System Habit SG Notes
6½ Black Metallic to submetallic PYROLUSITE
(Rutile Group)
MnO2		 Tetragonal Usually in earthy masses with a much lower hardness (2), but actual crystals are 6½, rare, short-prismatic to equant, usually in druzes of small crystals 5 May exhibit one perfect cleavage, prismatic. Most dendrites are not pyrolusite.
6 to 7 Black to Dark-brown, may also be Yellowish-grey, more rarely Red, White or Colorless Adamantine to metallic in crystals, greasy on fracture surfaces, may be earthy or submetallic in botryoids, concretions, and massive forms CASSITERITE
(Rutile Group)
SnO2		 Tetragonal Usually massive as botryoidal crusts or concretions ("wood tin"), crystals usually short prismatic and complexly twinned producing unusual shapes ("knees," stubby five-pointed "stars," etc.) 6.8 to 7.1  
6½ to 7 Grey to Bluish-grey, Brown to Honey-brown or Yellow to Golden-brown, more rarely Green or Violet Vitreous to sub-vitreous FERRO-AXINITE/
MANGANAXINITE
Ca2FeAl2BSi4O15(OH) 
Ca2MnAl2BSi4O15(OH)		 Triclinic Usually as thin wedge-shaped "axhead" crystals, often arranged in rosettes 3.23 to 3.32 (ferro-), 3.30 to 3.36 (mangan-) End members difficult to distinguish, though low end and high end S.G. may do the trick. Magnesio-axinite and tinzenite are two rare related species.
Hardness Color Luster Name System Habit SG Notes
6½ to 7 Pale-yellow to Olive-green to Olive-brown, Black Vitreous to sub-vitreous (forsterite) or submetallic to dull (fayalite) FAYALITE/
FORSTERITE
(Olivine Group)
Fe2(SiO4) 
Mg2(SiO4)		 Orthorhombic Usually as crystalline massive or granular, crystals short-prismatic 4.39 (fayalite) to 3.24 (forsterite) End members distinguished by S.G. and luster.   "Peridot" is the varietal name for gem material in the fayalite-forsterite series, usually forsterite.  

Table of Contents   Return to Step 13

Table IIIB-1: Nonmetallic Luster; Hardness 7 to 10; Has a Prominent Cleavage. (Can not be scratched by quartz.)
Cleavage Hardness Color Luster Name System Habit SG Notes
One  direction: Perfect (prismatic) 6 to 7 Grey, Green to Yellowish-green, Pinkish, Brown, Blue, Purple, Colorless Vitreous, may be pearly on cleavage surfaces ZOISITE
(Epidote Group)
Ca2Al3(SiO4)3(OH)		 Orthorhombic Usually in aggregates of crude parallel crystals with vertical striations on the faces, more rarely as well-formed prismatic crystals in clusters or singly 3.15 to 3.36 The blue gem variety "tanzanite" and pink gem variety "thulite" are rare.
One direction: Perfect (prismatic) 6½ to 7 Green to Yellow-green, Yellow, Grey, Brownish-green, Greenish-black, Black Vitreous to sub-vitreous, dull in weathered crystals and massive materials EPIDOTE
Ca2(Fe,Al)3(SiO4)3(OH)		 Monoclinic Usually in short to long prismatic crystals, may also be thick tabular or acicular (over 200 different forms are known), massive, coarse to fine granular, rarely fibrous 3.38-3.49 Commonest of the Epidote Group species.   Most of the Epidote group minerals may exhibit a second, poor, cleavage, but it is usually not seen.
Cleavage Hardness Color Luster Name System Habit SG Notes
One direction: Perfect (prismatic) 6½ to 7 Colorless to White, Grey, Pale-brown to Pale-yellow, more rarely Pale-blue to Pale-green Vitreous to sub-vitreous, silky in fibrous material, may be dull on weathered surfaces SILLIMANITE
Al2SiO5		 Orthorhombic Usually as crude prismatic crystals with a nearly square cross-section, surfaces often rough and altering to muscovite, may be in columnar to fibrous aggregates ("fibrolite") 3.23 to 3.27 Restricted to high-temperature and pressure metamorphic environments.
One direction: Perfect (prismatic) 6½ to 7 White to Greyish-white, Colorless, Pinkish-white to Pale-lavender, more rarely Greenish to Yellowish, Brown, Rose-red to Dark-red Vitreous to sub-adamantine, "brilliant" DIASPORE
AlO(OH)		 Orthorhombic Usually in thin platy crystalline aggregates, crystals thin, platy, may be prismatic or acicular, rarely tabular 3.35 to 3.45 Very brittle.  Often mistaken for milky to greyish quartz.
One direction: Perfect (pinacoidal, basal) 8 Colorless to Milky-white, Yellowish, to Brownish, Pinkish, Bluish, Greenish Vitreous, may be somewhat greasy on fracture surfaces TOPAZ
Al2SiO4(F,OH)2		 Orthorhombic Usually as stout prismatic to equant crystals, with or without pyramidal terminations 3.4 to 3.6 Largely restricted to granites, granite-pegmatites, and rhyolites.
Cleavage Hardness Color Luster Name System Habit SG Notes
Two  directions: Perfect in both directions (prismatic) 6 to 7 Dark-green to Medium-green to (more rarely) Pale-green, White to Grey or Bluish-grey, Lavender to Violet Vitreous to sub-vitreous, may be dull in granular material JADEITE
(Pyroxene Group)
Na(Al,Fe)Si2O6		 Monoclinic Usually in compact massive material, granular or short fibrous, with cleavage not apparent 3.24 to 3.43 Massive material often a mix of jadeite and diopside, crystals extremely rare. Jade in part (jade also includes nephrite variety of tremolite)
Two directions: Perfect in both directions (prismatic) 6½ to 7 Grey to White, Colorless, Tan, Yellow, Pale-green to Bright-green ("hiddenite"), Pink to Lilac to Violet ("kunzite") Vitreous to sub-vitreous SPODUMENE
(Pyroxene Group)
LiAlSi2O6		 Monoclinic Crystals are usually prismatic with a diamond shaped cross-section; but matrix-frozen crystals - the most commonly seen - tend to show only two adjacent faces, the other two not developed;  then they look like a triangular prism with two developed faces and a rough base to the 'triangle' - only half of the complete prism developed. 3.03 to 3.23 Crystals often very large, to 14 meters or more, crystals faces usually have a wood-grain look to them, gem quality material often with acid-etched crystal faces, heavily vertically striated.
Two directions: One perfect  (basal) and one good (prismatic) 6½ to 7 Colorless to White, more rarely Pale-yellow, Pale-pink or Pale-brown Vitreous BERTRANDITE
Be4Si2O7(OH)2		 Orthorhombic Usually as tiny to micro tabular crystals, also granular aggregates 2.57 to 2.63 Usually associated with beryl in pegmatites.  Cleavage often not seen
Cleavage Hardness Color Luster Name System Habit SG Notes
Three parting directions: Fair rhombohedral and basal (looks like cleavage on a small scale) 9 Dark-grey to Light-grey to Blue-grey to Blue (sapphire), Red (ruby), and Yellow, Brown and Green in sapphire Vitreous to sub-vitreous and dull CORUNDUM
Al2O3		 Trigonal Usually massive, granular (emery) and as barrel-shaped prismatic hexagonal crystals 4.0 Extremely hard – can only be scratched by moissanite (silicon carbide) and diamond.
Four  directions: Perfect in four directions (pyramidal) 10 Colorless to Yellow, Brown or Grey, may be Pink, Red, Blue, Green, and Black (due to inclusions) Adamantine DIAMOND
C		 Isometric Typically in octahedral crystals, usually appearing somewhat rounded on the edges, also as dodecahedral, tetrahedral, and cubic crystals, also often appearing somewhat rounded 3.50 to 3.53 Extremely hard – no other mineral or material will scratch it.  Gem material is limited to lamproites and kimberlites ("blue-earth") pipes and alluvial deposits eroded out of those pipes.

Table of Contents   Return to Step 14

Table IIIB-2: Nonmetallic Luster; Hardness 7 to 10; Cleavage not prominent.. (Can not be scratched by quartz.)
Hardness Color Luster Name System Habit SG Notes
6 to 7 Black to Dark-brown, may also be Yellowish-grey, more rarely Red, White or Colorless Adamantine to metallic in crystals, greasy on fracture surfaces, may be earthy or submetallic in botryoids, concretions, and massive forms CASSITERITE
(Rutile Group)
SnO2		 Tetragonal Usually massive as botryoidal crusts or concretions ("wood tin"), crystals usually short prismatic and complexly twinned producing unusual shapes ("knees", stubby five-pointed "stars," etc.) 6.8 to 7.1  
6½ to 7 Grey to Bluish-grey, Brown to Honey-brown or Yellow to Golden-brown, more rarely Green or Violet Vitreous to sub-vitreous FERRO-AXINITE/
MANGANAXINITE
Ca2FeAl2BSi4O15(OH)
Ca2MnAl2BSi4O15(OH)		 Triclinic Usually as thin wedge-shaped "axhead" crystals, often arranged in rosettes 3.23 to 3.32 (ferro-), 3.30 to 3.36 (mangan-) End members difficult to distinguish, though low end and high end S.G. may do the trick.  Magnesio-axinite and tinzenite are two rare related species.
6½ to 7 Pale-yellow to Olive-green to Olive-brown, Black Vitreous to sub-vitreous (forsterite) or submetallic to dull (fayalite) FAYALITE/
FORSTERITE
(Olivine Group)
Fe2(SiO4) 
Mg2(SiO4)		 Orthorhombic Usually as crystalline massive or granular, crystals short-prismatic 4.39 (fayalite) to 3.24 (forsterite) End members distinguished by S.G. and luster.  "Peridot" is the name for gem material in the fayalite-forsterite series, usually forsterite.  Names for intermediate members of the series, such as "chrysolite" and "hortonolite" are based on chemical composition and should not be used unless the composition is known.
Hardness Color Luster Name System Habit SG Notes
6½ to 7 Colorless to White, more rarely Pale-yellow, Pale-pink or Pale-brown Vitreous BERTRANDITE
Be4Si2O7(OH)2		 Orthorhombic Usually as tiny to micro tabular crystals, also granular aggregates 2.57 to 2.63 Usually associated with beryl in pegmatites.  May exhibit basal and prismatic cleavages.
7 Colorless, Milky, Smoky-grey to Black, Amethyst, Rose, Yellow to Brownish-yellow, may be tinted other shades by inclusions Vitreous QUARTZ
(Crystalline)
SiO2		 Trigonal Usually in pyramidally terminated prismatic hexagonal crystals or glassy massive, "rock crystal," "smoky" and "amethyst" varieties may be very large, "citrine" usually small to medium in size, "rose" usually rather small to micro-scale 2.65 Abundant! in milky and massive forms. Common in rock crystal, smoky and amethyst forms, citrine rare, rose crystals very rare. (See also immediately below for crypto- and non-crystalline forms.)
Hardness Color Luster Name System Habit SG Notes
7 Colorless, Milky, Grey to Black, Red, Yellow to Brownish-yellow, Brown, Green, Blue, may be tinted other shades by inclusions Vitreous to waxy to dull QUARTZ
(Crypto- and Non-crystalline)
SiO2		 Trigonal "Chalcedony" as cryptocrystalline fibrous amorphous to sub-botryoidal masses, un-banded or un-patterned, with a waxy luster ("carnelian" is red, "chrysoprase" is green due to nickel, "heliotrope" or "bloodstone" is green with small red jasper flecks in it, "sard" is brown); "chalcedony, sub-variety agate" in circular, concentrically banded to intricately patterned masses with considerable color variation in single samples, waxy to vitreous luster; "chalcedony sub-variety onyx" has parallel layers instead of concentric ones ("sardonyx" has alternating white and black layers). 2.65 In massive, non- crystalline forms: "Jasper" red or blue, rarely yellow, dull luster; "flint" dark grey to black, dull to sub-vitreous luster; "chert" medium to light grey, dull to sub-vitreous luster; "aventurine" green due to inclusions, vitreous luster.
Hardness Color Luster Name System Habit SG Notes
7 Colorless, Milky-white, Pale-grey, Yellowish, and Brownish Vitreous CRISTOBALITE
SiO2		 Tetragonal (pseudo Isometric) Usually as micro-spherical aggregates, may be botryoidal or stalactic, crystals very rare, usually micro-octahedra 2.2 to 2.33 Largely restricted to siliceous volcanic rocks. Cristobalite is only partially stable at typical terrestrial temperatures, inverting to quartz.  Most finds are actually quartz pseudomorphs of the original crystals
7 Colorless, Milky-white Vitreous TRIDYMITE
SiO2		 Orthorhombic & Hexagonal Usually as thin to thick tabular or twinned pseudo-hexagonal crystals 2.26 to 2.33 Largely restricted to felsic volcanic rocks; Tridymite is only partially stable at typical terrestrial temperatures, inverting to quartz.  Most finds are actually quartz pseudomorphs of the original crystals
7 to 7½ Black to Bluish-black or Brownish-black or Greenish-black Vitreous to sub-vitreous, may appear somewhat oily on fracture surfaces SCHORL /
UVITE
(Tourmaline Group)
NaFe3Al6 (BO3)3(Si6O18)(OH)4
(Ca,Na)(Mg,Fe)3Al5Mg(BO3)3(Si6O18)(OH,F)4		 Trigonal Schorl usually in stout to long-prismatic six-sided crystals with a nearly triangular cross-section. Uvite usually in stubby short-prismatic crystals, sometimes appearing almost pyramidal or dipyramidal, but may take identical habits. Both may also be massively crystalline or granular. 3.13 (schorl)
2.96 to 3.06 (uvite)		 These two end members are best distinguished by their S.G.s.  Foitite, feruvite, and povondrite are three rare to very rare black Tourmaline Group members.
Hardness Color Luster Name System Habit SG Notes
7 to 7½ Black to Brownish-black or Brown Vitreous to sub-vitreous, may appear oily on fracture surfaces DRAVITE
(Tourmaline Group)
NaMg3Al6(BO3)3(Si6O18)(OH)4		 Trigonal Usually as stout prismatic six-sided crystals, often with a pyramidal termination at one end and a pedial termination at the other 2.9 to 3.3 Largely restricted to marbles, schists and slates.  Best distinguished from schorl and uvite by environment when black. Buergerite is a rare bronze-brown Tourmaline Group member.
7 to 7½ Dark emerald-green to Greenish-black to Black Vitreous, may appear oily on fracture surfaces CHROMEDRAVITE
(Tourmaline Group)
NaMg3(Cr,Fe)6 (BO3)3 (Si6O18)(OH)4		 Trigonal Usually as small to tiny nearly equant short-prismatic crystals and grains 3.39 to 3.40 Usually distinguished by its deep emerald green color – largely restricted to chromium bearing micaceous metasomatites.  Very rare.  Distinguished from dark greenish-black schorl or uvite by its higher S.G
7 to 7½ Light- to Medium-green, Pink to Red, Light- to Medium-blue to Dark-blue, more rarely Light-brown to Yellow, Colorless Vitreous to oily ELBAITE
(Tourmaline Group)
Na(Li,Al)3Al6 (BO3)3(Si6O18)(OH)4		 Trigonal Usually in slender prismatic six-sided crystals with a nearly triangular cross-section, often appearing somewhat rounded. Whole crystals may be hemimorphic, with different shaped terminations (pyramidal and pedial) at opposite ends 3.05 to 3.10 Distinguished from most other Tourmaline Group species by its lighter colors – also, largely restricted to granite-pegmatites.  Dark-blue elbaite is almost impossible to distinguish from dark blue schorl, and both can occur together.  Olenite, pale pink, and liddicoatite, light-pink or light-green, are two rare to very rare colored Tourmaline Group species.
Hardness Color Luster Name System Habit SG Notes
7 to7½ Deep-green to "Rusty"-green Vitreous UVAROVITE
(Garnet Group)
Ca3Cr2(SiO4)3		 Isometric Usually as small to tiny dodecahedral crystals 3.40 to 3.83 Largely restricted to chrome-bearing deposits, particularly serpentinite ultramafics containing chromite.  Rare. Goldmanite and knorringite are very rare dark-green and blue-green Garnet Group species, but are found in different mineral environments than uvarovite.
7 to7½ Pink to Red, Brownish-orange to Orange, Cinnamon, Yellow to Yellow-green, Pale-green to Grass-green to Emerald-green, Colorless Vitreous GROSSULAR
(Garnet Group)
Ca3Al2(SiO4)3		 Isometric Usually as small dodecahedral crystals 3.42 to 3.80 Largely found in contact and regionally metamorphosed impure calcareous rocks, and in serpentinite and rodingite ultramafic rocks.  Hibschite and katoite are very rare Garnet Group species that can be similar greens or milky to colorless, but they are found in different mineral environments than grossular.
7 to7½ Brown, Brownish-red to Brownish-yellow, Yellow to Yellow-green, Greyish-green to Medium- or Deep-green, Black Vitreous ANDRADITE
(Garnet Group)
Ca3Fe2(SiO4)3		 Isometric Usually as small to medium sized dodecahedral crystals 3.45 Usually from Ca and Fe rich contact metamorphic rocks and skarns, also from alkaline and ultrabasic igneous rocks.  Calderite is a very rare Garnet Group species with color similar to andradite, but it is found in a different mineral environment.
Hardness Color Luster Name System Habit SG Notes
7 to 7½ Black to Brownish-black Vitreous SCHORLOMITE
(Garnet Group)
Ca3Ti2(Fe2Si)O12		 Isometric Usually as small dodecahedral crystals 3.77 to 3.93 Largely restricted to alkaline igneous rocks.  Morimotoite and kimzeyite are very rare Garnet Group species that may be the same color as schorlomite, but they are found in different environments
7 to 7½ Dark-red to Violet-red or Deep rose-red, also Reddish-orange Vitreous PYROPE
(Garnet Group)
Mg3Al2(SiO4)3		 Isometric Usually as small to tiny dodecahedral crystals 3.65 to 3.82 Usually found in high temperature and high pressure metamorphic rocks, ultrabasic igneous rocks, and kimberlites and peridotites.  Uncommon.  Majorite is a very rare Garnet Group species that can be purplish-violet, but is found in a different environment than pyrope.
7 to 7½ Brown to Brownish-red to Red, Violet-red or Orangish-red Vitreous ALMANDINE
(Garnet Group)
Fe3Al2(SiO4)3		 Isometric Usually as dodecahedral crystals 3.85 to 4.20 Occurs in a number of metamorphic and igneous environments – most common of the Garnet Group species.
Hardness Color Luster Name System Habit SG Notes
7 to 7½ Orangish-red to Reddish-orange, Rose-red to Ruby-red or Hyacinth-red, Reddish-brown, Pale-yellow Vitreous SPESSARTINE
(Garnet Group)
Mn3Al2(SiO4)3		 Isometric Usually as medium to tiny dodecahedral crystals 3.90 to 4.20 Occurs in metamorphic and igneous rocks rich in Mn.
7 to 7½ Medium- to Dark-brown, Reddish-brown Vitreous to sub-vitreous, may also be dull STAUROLITE
(Fe,Mg,Zn)2Al9(Si,Al)4O22(OH)2		 Monoclinic pseudo. Orthorhombic Usually as either short- to long-prismatic crystals, frequently twinned ("fairy crosses"), with twining at either 90o or 60o 3.74 to 3.83 Usually in intermediate grade pelitic metamorphic rocks
7 to 7½ Greyish-blue to Blue, Grey, Greenish-blue, Violet Vitreous to oily CORDIERITE
(Beryl Group?)
(Mg,Fe)2Al3[AlSi5O18] . H2O		 Orthorhombic Usually granular or massively crystalline aggregates, crystals short-prismatic 2.53 to 2.65 Largely restricted to contact metamorphic rocks and high-grade regional metamorphic rocks.
7½ Reddish-brown to Pale-pink to Deep-pink/Flesh-colored, White to Grey to Bluish-grey to Blue, Olive-green, Green, Violet, Yellow Vitreous to sub-vitreous, may be dull ANDALUSITE
Al2SiO5		 Orthorhombic Usually as prismatic crystals with a nearly square cross-section, may be tapered in both directions from the center and exhibit a cross-like pattern on the cross section due to carbonaceous inclusions ("chiastolite") 3.13 to 3.21 Largely a mineral of low to intermediate grade metamorphic rocks, but also known from granites and granite-pegmatites
Hardness Color Luster Name System Habit SG Notes
7½ Brown, White, Yellow, Orange, Green, Blue Adamantine, oily on fracture surfaces ZIRCON
ZrSiO4		 Tetragonal Usually as small tetragonal prisms with pyramidal terminations, may also be bipyramidal without the prism 4.6 to 4.71 Fluoresces orange-yellow, yellow and orange. This mineral may also be metamict (structurally disrupted by radiation) and then exhibits a lower H. (6 to 7) and S.G  3.9 to 4.6 range.
7½ to 8 Pale-blue to Pale-green (gem: "aquamarine")
Yellow to Golden-yellow (gem: "heliodore"),
Pink to light-red (gem: "morganite"),
White to Tan,
Emerald-green (gem: "emerald")
Colorless		 Vitreous BERYL
Be3Al2Si6O18		 Hexagonal Usually as stout prismatic hexagonal crystals, also granular in matrix 2.63 to 2.78 Most often found in granite-pegmatites and rhyolites, but known from other environments as well.
Hardness Color Luster Name System Habit SG Notes
7½ to 8 White to Colorless Vitreous PHENAKITE
Be2SiO4		 Trigonal Usually massive, granular, and as modified flattened rhombs, more rarely as prismatic crystals 2.97 to 3.0 Usually found with beryl in pegmatites.
7½ to 8 Dark-green to Greenish-black, more rarely Dark-yellow to Pale-yellow Vitreous to sub-vitreous, may be dull GAHNITE
(Spinel Group)
ZnAl2O4		 Isometric Usually massive, granular, also as octahedral crystals, may be rounded or sharp 4.57 Usually in high-temperature ore deposits in crystalline schists or in pegmatites.
7½ to 8 Red, Black, Brown, Blue, Green Vitreous to sub-vitreous SPINEL
MgAl2O4		 Isometric Usually massive, granular, and as octahedral crystals, often twinned 3.56 Distinguished from gahnite by it's lower specific gravity
8½ Yellow to Emerald-green Vitreous CHRYSOBERYL
BeAl2O4		 Orthorhombic Usually as tabular or prismatic crystals, often twinned in heart or fish-tail shapes, may also be cyclically twinned in pseudo-hexagonal crystals 3.75 May appear red or brownish-pink in incandescent light ("alexandrite").
9 Dark-grey to Light-grey to Blue-grey to Blue (sapphire), Red (ruby), and Yellow, Brown and Green (sapphire) Vitreous to sub-vitreous and dull CORUNDUM
Al2O3		 Trigonal Usually massive, granular (emery) and as barrel-shaped prismatic hexagonal crystals 4.0 Extremely hard – can only be scratched by moissanite (silicon carbide) and diamond.

Notes:
The Tourmaline Group species can be difficult to tell apart without specific locality data.  The overlap of color and habit can make crystals without matrix very difficult to distinguish without lab tests.

Most of the Garnet Group species can be very difficult to tell apart.  Color alone is rarely – if ever – diagnostic; and S.G.s overlap too much to make them useful alone or with color.  Mineral environment information is usually needed in conjunction with S.G. and color to even begin to guess the species.  The best bet is specific knowledge of what is found at any given locality – or lab tests in the absence of that. (Far too many "visual identifications" prove to be wrong…)

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Copyright

This "Mineral Identification Key" is copyrighted by Alan Plante, Donald Peck and David Von Bargen, 2003; all rights reserved.  Permission to copy all or parts of the Key is  granted for noncommercial use by individuals and mineral clubs, study groups, or educational institutions.  Publication  in any medium for profit, including print and electronic, is expressly prohibited, except by written permission from the authors.  Permission is required before posting a copy of the Key to another web site.

Alan Plante, 8 Hamlin Avenue, Gorham, NH 03581
Donald Peck, 6 Indian Rock Road, Warren, NJ 07059
David Von Bargen, 9730 W. Layton Ave., Milwaukee, WI 53228

[ Table of Contents ] [ Introduction ] [ Identification Kit ] [ Mineral Properties ] [ Environments & Associations ] [ In Conclusion ] [ The Mineral ID Key ]

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