Botallackite
Botallackite, chemical formula Cu2(OH)3Cl is a secondary copper mineral, named for its type locality at the Botallack Mine, St Just in Penwith, Cornwall. It is polymorphous with atacamite, paratacamite and clinoatacamite.
| Botallackite | |
|---|---|
Botallackite from the Levant Mine, Cornwall | |
| General | |
| Category | Halide minerals |
| Formula (repeating unit) | Cu2(OH)3Cl |
| IMA symbol | Blk |
| Strunz classification | 3.DA.10b |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (same H-M symbol) |
| Space group | P21/m |
| Unit cell | a = 5.717 Å, b = 6.126 Å, c = 5.636 Å; β = 93.07°; Z = 2 |
| Identification | |
| Colour | Shades of green |
| Crystal habit | Platy interlaced crystal crusts |
| Cleavage | {100} Perfect |
| Mohs scale hardness | Soft |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 3.6 |
| Optical properties | Biaxial (+) |
| Refractive index | nα= 1.775, nβ= 1.800, nγ= 1.846 |
| Birefringence | δ = 0.071 |
| Pleochroism | Weak – blue green shades |
| Dispersion | r > v, strong |
| References | |
Botallackite crystallises in the monoclinic crystal system. It is mountain-green to green in colour, with one distinct to good cleavage.
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