Atacamite

Atacamite
	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	[1][2][3][4]

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.

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]

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References

Atacamite on Mindat.org
Handbook of Mineralogy
Atacamite on Webmineral
Mineralienatlas
"Atacamite - CAMEO". cameo.mfa.org. Retrieved 2017-10-15.
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.

External links

Mineral galleries

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[Mindat-1] Atacamite on Mindat.org

[HBM-2] Handbook of Mineralogy

[Webmin-3] Atacamite on Webmineral

[4] Mineralienatlas

[:0-5] "Atacamite - CAMEO". cameo.mfa.org. Retrieved 2017-10-15.

[Lichtenegger-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.