Descloizite
From Wikipedia, the free encyclopedia
| Descloizite | |
|---|---|
 Descloizite specimen from Berg Aukas (Berg Aukus), Namibia, 9.5 x 8.9 x 4.9 cm | |
| General | |
| Category | Vanadate mineral |
| Formula | (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] |
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.
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]
