| Atacamite | |
| Category: | Halide mineral |
| Formula: | Cu2Cl(OH)3 |
| Imasymbol: | Ata[1] |
| Strunz: | 3.DA.10a |
| System: | Orthorhombic |
| Class: | Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m) |
| Symmetry: | Pnma |
| Unit Cell: | a = 6.03, b = 9.12 c = 6.865 [Å]; Z = 4 |
| Color: | Bright green, dark emerald-green to blackish green |
| Habit: | Slender prismatic crystals, fibrous, granular to compact, massive |
| Twinning: | Contact and penetration with complex twinned groupings |
| Cleavage: | Perfect on, fair on |
| Fracture: | Conchoidal |
| Tenacity: | Brittle |
| Mohs: | 3–3.5 |
| Luster: | Adamantine to vitreous |
| Streak: | Apple green |
| Diaphaneity: | Transparent to translucent |
| Gravity: | 3.745–3.776 |
| Opticalprop: | Biaxial (−) |
| Refractive: | nα = 1.831 nβ = 1.861 nγ = 1.880 |
| Birefringence: | δ = 0.049 |
| Pleochroism: | X = pale green; Y = yellow-green; Z = grass-green |
| 2V: | Calculated: 74° |
| Dispersion: | r < v, strong |
| References: | [2] [3] [4] [5] |
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 1802 by Dmitri de Gallitzin. The Atacama Desert is also the namesake of the mineral.
Atacamite is polymorphous with botallackite, clinoatacamite, and paratacamite. 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. The mineral has also been found naturally on oxidized copper deposits in Chile, China, Russia, Czech Republic, Arizona, and Australia. It occurs in association with cuprite, brochantite, linarite, caledonite, malachite, chrysocolla and its polymorphs.
Atacamite has been discovered in the patina of the Statue of Liberty, and as alteration of ancient bronze and copper artifacts. The mineral has been found as a pigment in sculpture, manuscripts, maps, and frescoes discovered in Eurasia, Russia, and Persia.[6]
Atacamite occurs as a biomineral in the jaws of bloodworms.[7] [8]