Atacamite

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 by D. de Fallizen.[1][5] The Atacama Desert is also the namesake of the mineral.

Atacamite
Atacamite prisms from Chile
General
CategoryHalide mineral
Formula
(repeating unit)		Cu2Cl(OH)3
Strunz classification3.DA.10a
Crystal systemOrthorhombic
Crystal classDipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space groupPnma
Unit cella = 6.03, b = 9.12
c = 6.865 [Å]; Z = 4
Identification
ColorBright green, dark emerald-green to blackish green
Crystal habitSlender prismatic crystals, fibrous, granular to compact, massive
TwinningContact and penetration with complex twinned groupings
CleavagePerfect on {010}, fair on {101}
FractureConchoidal
TenacityBrittle
Mohs scale hardness3 - 3.5
LusterAdamantine to vitreous
StreakApple green
DiaphaneityTransparent to translucent
Specific gravity3.745 – 3.776
Optical propertiesBiaxial (-)
Refractive indexnα = 1.831 nβ = 1.861 nγ = 1.880
Birefringenceδ = 0.049
PleochroismX = pale green; Y = yellow-green; Z = grass-green
2V angleCalculated: 74°
Dispersionr < v, strong
References[1][2][3][4]

Occurrence

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.[2] The mineral has also been found naturally on oxidized copper deposits in Chile, China, Russia, Czech Republic, Arizona, and Australia.[5] It occurs in association with cuprite, brochantite, linarite, caledonite, malachite, chrysocolla and its polymorphs.[2]

Atacamite from Mt. Gunson, South Australia

It has been shown that atacamite is a component of the jaws of some Glycera species.[6]

Synthetic Occurrence

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.[5]

References
  1. Atacamite on Mindat.org
  2. Handbook of Mineralogy
  3. Atacamite on Webmineral
  4. Mineralienatlas
  5. "Atacamite - CAMEO". cameo.mfa.org. Retrieved 2017-10-15.
  6. 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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