Chemistry:Atacamite

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Short description: Halide evaporite mineral
Atacamite
Atacamite on malachite - Mt Gunson mines, South Australia.jpg
Atacamite from Mt. Gunson mines, South Australia
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
|re|er}}Adamantine 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]

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.[1] 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 .[6] It occurs in association with cuprite, brochantite, linarite, caledonite, malachite, chrysocolla and its polymorphs.[2]

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.[6]

Biomineral

Atacamite occurs as a biomineral in the jaws of bloodworms.[7][8]

References

  1. Jump up to: 1.0 1.1 1.2 Atacamite on Mindat.org
  2. Jump up to: 2.0 2.1 2.2 Handbook of Mineralogy
  3. Atacamite on Webmineral
  4. Mineralienatlas
  5. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine 85 (3): 291–320. doi:10.1180/mgm.2021.43. Bibcode2021MinM...85..291W. 
  6. Jump up to: 6.0 6.1 "Atacamite – CAMEO" (in en). http://cameo.mfa.org/wiki/Atacamite. 
  7. "High abrasion resistance with sparse mineralization: copper biomineral in worm jaws". Science 298 (5592): 389–92. October 2002. doi:10.1126/science.1075433. PMID 12376695. Bibcode2002Sci...298..389L. 
  8. "Zinc and mechanical prowess in the jaws of Nereis, a marine worm". Proc. Natl. Acad. Sci. U.S.A. 100 (16): 9144–9. August 2003. doi:10.1073/pnas.1632658100. PMID 12886017. Bibcode2003PNAS..100.9144L. 

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