- Atacamite
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Atacamite
Atacamite prisms from ChileGeneral Category Halide mineral Chemical formula Cu2Cl(OH)3 Strunz classification 03.DA.10a Crystal symmetry Orthorhombic dipyramidal
H-M symbol: (2/m 2/m 2/m)
Space group: PmcnUnit 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 Crystal system Orthorhombic 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]
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