Mineral Identification Key

The Mineral Identification Key

Copper, Michigan, Seaman Museum specimen

Table IIIB-1: Nonmetallic Luster; Hardness 7 to 10; Has a Prominent Cleavage. (Can not be scratched by quartz.) [Previous Table] [Next Table]

Cleavage Hardness Color Luster Name System Habit SG Notes

One direction: Perfect 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 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 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 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.

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Cleavage	Hardness	Color	Luster	Name	System	Habit	SG	Notes
One direction: Perfect	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	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	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	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.