Atacamite
| Atacamite | |
|---|---|
 Atacamite prisms from Chile | |
| General | |
| Category | Halide mineral |
| Formula (repeating unit) | Cu2Cl(OH)3 |
| Strunz classification | 03.DA.10a |
| Crystal system | Orthorhombic |
| Space group | Orthorhombic dipyramidal H-M symbol: (2/m 2/m 2/m) Space group: Pmcn |
| Unit cell | a = 6.03 Å, b = 9.12 Å, c = 6.865 Å; Z = 4 |
| Identification | |
| Color | Bright green, dark emerald-green to blackish green |
| Crystal habit | Slender prismatic crystals, fibrous, granular to compact, massive |
| Twinning | Contact and penetration with complex twinned groupings |
| Cleavage | Perfect on {010}, fair on {101} |
| Fracture | Conchoidal |
| Tenacity | Brittle |
| Mohs scale hardness | 3 - 3.5 |
| Luster | Adamantine to vitreous |
| Streak | Apple green |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 3.745 – 3.776 |
| Optical properties | Biaxial (-) |
| Refractive index | nα = 1.831 nβ = 1.861 nγ = 1.880 |
| Birefringence | δ = 0.049 |
| Pleochroism | X = pale green; Y = yellow-green; Z = grass-green |
| 2V angle | Calculated: 74° |
| Dispersion | r < v, strong |
| References | [1][2][3] |
Atacamite is a copper halide mineral: a copper(II) chloride hydroxide with formula Cu2Cl(OH)3.
It was first described for deposits in the Atacama Desert of Chile in 1801.[1]
Atacamite is polymorphous with botallackite, clinoatacamite, and paratacamite.[1] Atacamite is a comparatively rare mineral, formed from primary copper minerals in the oxidation or weathering zone of arid climates. It has also been reported from fumarole deposits, as sulfide alteration products in black smokers and as alteration of ancient bronze and copper artefacts.[2] It occurs in association with cuprite, brochantite, linarite, caledonite, malachite, chrysocolla and its polymorphs.[2]
References
Wikimedia Commons has media related to Atacamite.