Mineral Identification Guide: Properties of Olivine, Andalusite, Epidote, Tourmaline and More

Silicate Mineral Properties

Olivine: SiO₄ (Mg,Fe)

Rhombic. Conchoidal, fragile. Olive green, beige, white to gray. Vitreous, translucent to maroon transparent. Hardness 6–7.

Blanca (SiO₄)₃ A₃ B₂ cubic, conchoidal, irregular, fragile. Red, reddish black, sometimes pink or purple. Vitreous and resinous, transparent to translucent. Hardness 7.

Andalusite: SiO₄ Al AlO (orthorhombic)

Irregular to subconchoidal, fragile. White, gray, red, brown, green. Vitreous, often matte, transparent to translucent. Hardness 7–5. White.

Epidote: Sorosilicate

Green, monoclinic, irregular, fragile. Olive green, gray-green to yellow-green. Vitreous, transparent to translucent. Hardness 6–7. Clear to gray.

Tourmaline: Cyclosilicate, hexagonal

Irregular, conchoidal, fragile. Black, brown, blue, clear. Vitreous, transparent. Hardness 7 to 7.5. White.

Beryl: Be₃Al₂Si₆O₁₈

Hexagonal, irregular, fragile. Green, teal, yellow or white, red, pink, blue. Vitreous, transparent to translucent. Hardness 7–8. Clear.

Dioptase: (Si₆O₁₈) Cu₆ 6H₂O

Rhombohedral, conchoidal, translucent. Hardness 5. Green.

Chrysocolla

Irregular, fragile. Emerald green, vitreous, transparent.

Chrysocolla A: CuSiO₃ nH₂O

Cryptocrystalline, fibrous, conchoidal, somewhat sectile, fragile. Green or blue, brown or black when it contains iron oxide. Copper-ore vitreous, earthy, translucent to opaque. Hardness 2–4. Pure white if present.

Enstatite: (Si₂O₆) Mg

Rhombic, good, fragile. Grayish, yellowish or greenish. Chestnut vitreous to pearly, translucent. Hardness 5. White.

Augite: Monoclinic pyroxene

Basal parting, fragile. Green foil, dark, showing a clear black. Vitreous, translucent. Hardness 5–6. White.

Actinolite (Tremolite): Amphibole

Columnar or fibrous, irregular, fragile. Green and greyish green, bright, white, black. Vitreous (silky), clear to translucent. Hardness 5–6. Blanca (clear).

Hornblende: Amphibole

Monoclinic, prismatic, irregular, fragile. Green, dark to blackish. Vitreous (fibrous, silky), translucent. Hardness 5–6. White (clear).

Talc (Si₄O₁₀) Mg₃(OH)₂

Monoclinic, prismatic, irregular, sectile. Apple green, gray, white, or green soapstone gray. Pearly to greasy, translucent. Hardness 1. White.

Biotite: (Al,Si₃O₁₀) K(Mg,Fe)₃(OH)₂

Monoclinic, irregular, flexible and elastic. Dark green, dark brown to black, yellow clear. Pearly, submetallic, vitreous, transparent to translucent. Hardness 3. Colorless (white).

Muscovite (AlSi₃O₁₀) K Al₂(OH)₂

Monoclinic, prismatic, irregular, elastic, flexible. White, clear, green, pink, or brown. Vitreous to silky pearly, transparent to translucent (in thicker blocks). Hardness 2. Colorless.

Kaolinite (Si₄O₁₀) Al₄(OH)₈

Monoclinic, irregular, conchoidal, flexible and inelastic. White, often due to various colors from impurities. Earthy, matte (pearly), transparent to translucent. Hardness 2. White.

Quartz: SiO₂

Hexagonal, conchoidal, subconchoidal, brittle. Hard, colorless or white, with varieties. Vitreous (fatty, resplendent), transparent to translucent. Hardness 7. White.

Orthoclase (Al, Si₃O₈) K

Monoclinic, conchoidal to irregular, brittle to fragile. Colorless or white, gray, red, flesh. Vitreous to pearly, transparent. Hardness 6. White, clear.