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 as a volcanic sublimate 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]
It has been shown that atacamite is a component of the jaws of some Glycera species.[4]
References
- ^ a b c Atacamite on Mindat.org
- ^ a b c Handbook of Mineralogy
- ^ Atacamite on Webmineral
- ^ Lichtenegger HC, Schöberl T, Bartl MH, Waite H, Stucky GD (October 2002). "High abrasion resistance with sparse mineralization: copper biomineral in worm jaws". Science. 298 (5592): 389–92. Bibcode:2002Sci...298..389L. doi:10.1126/science.1075433. PMID 12376695.
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