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Atacamite

Atacamite
Atacamit-chile-Copiapo-Stefan.jpg
Atacamite prisms from Chile
General
Category Halide mineral
Formula
(repeating unit)
Cu2Cl(OH)3
Strunz classification 3.DA.10a
Crystal system Orthorhombic
Crystal class Dipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space group Pnma
Unit cell a = 6.03, b = 9.12
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

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.

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 and as alteration of ancient bronze and copper artefacts. It occurs in association with cuprite, brochantite, linarite, caledonite, malachite, chrysocolla and its polymorphs.

It has been shown that atacamite is a component of the jaws of some Glycera species.



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