Descloizite
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. Appreciable gallium and germanium may also be incorporated into the crystal structure.
| Descloizite | |
|---|---|
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 |
| 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 | |
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. There is also an arsenate analogue called arsendescloizite.
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