The Mineral Identification Key Copper, Michigan, Seaman Museum specimen

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) [Previous Table [Next Table
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)
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
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/

MgAl2(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
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/

(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.
Light-green to Yellow-green, Yellow-brown to Reddish-brown, Colorless Vitreous, to resinous WILLEMITE
(Phenakite Group)
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
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
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)
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
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)
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
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)
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
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
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
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
Black Metallic to submetallic PYROLUSITE
(Rutile Group)
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)
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/
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/

(Olivine Group)
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.  

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