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Descloizite
Mineral / From Wikipedia, the free encyclopedia
Descloizite is a rare mineral species consisting of basic lead and zinc vanadate, (Pb, Zn)2(OH)VO4, crystallizing in the orthorhombic crystal system and isomorphous with olivenite.[5] Appreciable gallium and germanium may also be incorporated into the crystal structure.
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Descloizite | |
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![]() Descloizite specimen from Berg Aukas (Berg Aukus), Namibia, 9.5 x 8.9 x 4.9 cm | |
General | |
Category | Vanadate mineral |
Formula (repeating unit) | (Pb,Zn)2VO4OH |
IMA symbol | Dcz[1] |
Strunz classification | 8.BH.40 |
Crystal system | Orthorhombic |
Crystal class | Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m) |
Space group | Pnma (no. 62) |
Unit cell | a = 7.593, b = 6.057 c = 9.416 [Å]; Z = 4 |
Identification | |
Color | Brownish red, red-orange, reddish to blackish brown, nearly black |
Crystal habit | Zoned tabular crystals common, encrustations and plumose aggregates |
Cleavage | None |
Fracture | Irregular, sub-conchoidal |
Tenacity | Brittle |
Mohs scale hardness | 3 – 3.5 |
Luster | Greasy |
Streak | Orange to brownish red |
Diaphaneity | Transparent to opaque |
Specific gravity | 6.1 – 6.2 |
Optical properties | Biaxial (−) |
Refractive index | nα = 2.185 nβ = 2.265 nγ = 2.350 |
Birefringence | δ = 0.165 |
Pleochroism | Visible |
2V angle | 85° to 90° |
Dispersion | Strong r > v rarely r < v |
References | [2][3][4] |
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The color is deep cherry-red to brown or black, and the crystals are transparent or translucent with a greasy lustre; the streak is orange-yellow to brown; specific gravity 5.9 to 6.2; hardness 31/2. A variety known as cuprodescloizite is dull green in color; it contains a considerable amount of copper replacing zinc and some arsenic replacing vanadium.[5] There is also an arsenate analogue called arsendescloizite.[6]