Fluorite | |
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![]() Deep green isolated fluorite crystal resembling a truncated octahedron, set upon a micaceous matrix, from Erongo Mountain, Erongo Region, Namibia (overall size: 50 mm x 27 mm, crystal size: 19 mm wide, 30 g)
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General | |
Category | Halide mineral |
Formula (repeating unit) |
CaF2 |
Strunz classification | 3.AB.25 |
Crystal system | Isometric |
Crystal class |
Hexoctahedral (m3m) H–M symbol: (4/m 3 2/m) (cF12) |
Space group | Fm3m (No. 225) |
Unit cell | a = 5.4626 Å; Z = 4 |
Identification | |
Color | Colorless, although samples are often deeply colored owing to impurities. |
Crystal habit | Well-formed coarse sized crystals; also nodular, botryoidal, rarely columnar or fibrous; granular, massive |
Twinning | Common on {111}, interpenetrant, flattened |
Cleavage | Octahedral, perfect on {111}, parting on {011} |
Fracture | Subconchoidal to uneven |
Tenacity | Brittle |
Mohs scale hardness | 4 (defining mineral) |
Luster | Vitreous |
Streak | White |
Diaphaneity | Transparent to translucent |
Specific gravity | 3.175–3.184; to 3.56 if high in rare-earth elements |
Optical properties | Isotropic; weak anomalous anisotropism |
Refractive index | 1.433–1.448 |
Fusibility | 3 |
Solubility | slightly water soluble and in hot hydrochloric acid |
Other characteristics | May be fluorescent, phosphorescent, thermoluminescencent, and/or triboluminescent |
References |