 |
The Mineral Identification Key |  |
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The Mineral Identification Key | |
Table IIB-1: Streak not colored, Cleavage Prominent, Hardness less than 2½: (Can be scratched with a fingernail, Streak: white or none.) [Previous Table] [Next Table]
| 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) (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 |
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