Atacamite

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Atacamite
Atacamite on malachite - Mt Gunson mines, South Australia.jpg
Atacamite from Mt. Gunson mines, South Australia
General
Category Halide mineral
Formula Cu2Cl(OH)3
IMA symbol Ata [1]
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
ColorBright 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 hardness3–3.5
Luster Adamantine to vitreous
Streak Apple green
Diaphaneity Transparent to translucent
Specific gravity 3.745–3.776
Optical propertiesBiaxial (−)
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 [2] [3] [4] [5]

Atacamite is a copper halide mineral: a copper(II) chloride hydroxide with formula Cu2Cl(OH)3. It was first described from deposits in the Atacama Desert of Chile in 1802 by Dmitri Alekseyevich Golitsyn. [2] The Atacama Desert is also the namesake of the mineral.

Contents

Occurrence

Atacamite is polymorphous with botallackite, clinoatacamite, and paratacamite. [2] 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. [3] 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, and chrysocolla and its polymorphs. [3]

Synthetic occurrence

Atacamite has been discovered in the patina of the Statue of Liberty, and as alteration of ancient bronze and copper artifacts. The bronze of the Antikythera mechanism had turned to atacamite under the sea. [7]

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. [8]

References

  1. ↑ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi: 10.1180/mgm.2021.43 . S2CID   235729616.
  2. 1 2 3 Atacamite on Mindat.org
  3. 1 2 3 Handbook of Mineralogy
  4. ↑ Atacamite on Webmineral
  5. ↑ Mineralienatlas
  6. 1 2 "Atacamite – CAMEO". cameo.mfa.org. Retrieved 15 October 2017.
  7. ↑ Alex Wilkins (17 April 2025). "Ancient computer's gears may not have been able to turn". New Scientist.
  8. ↑ 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. S2CID   14001250.
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