Aurichalcite

Aurichalcite is a carbonate mineral, usually found as a secondary mineral in copper and zinc deposits. Its chemical formula is (Zn,Cu)5(CO3)2(OH)6. The zinc to copper ratio is about 5:4.[2]

Aurichalcite
General
CategoryCarbonate mineral
Formula
(repeating unit)		(Zn,Cu)5[(OH)3|CO3]2
Strunz classification5.BA.15
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupP21/m
Unit cella = 13.82, b = 6.419
c = 5.29 [Å]
β = 101.04°; Z = 2
Identification
ColorPale green, greenish blue, sky-blue; colorless to pale blue, pale green in transmitted light
Crystal habitTypically in tufted divergent sprays or spherical aggregates, may be in thick crusts; rarely columnar, laminated or granular
TwinningObserved in X-ray patterns
Cleavage{010} and {100} Perfect
FractureUneven
Mohs scale hardness2
LusterPearly, silky
StreakLight blue
DiaphaneityTransparent
Specific gravity3.96
Optical propertiesBiaxial (-)
Refractive indexnα = 1.655 nβ = 1.740 nγ = 1.744
Birefringence0.0890
PleochroismWeak colorless to pale green
2V angleMeasured: 1° to 4°, Calculated: 22°
References[1][2][3]

Occurrence

Aurichalcite typically occurs in the oxidized zone of copper and zinc deposits. Associated minerals include: rosasite, smithsonite, hemimorphite, hydrozincite, malachite and azurite.[1]

It was first described in 1839 by Bottger who named the mineral for its zinc and copper content after the Greek όρειχαλκος, for "mountain brass" or "mountain copper", the name of a fabulous metal. The type locality is the Loktevskoye Mine, Upper Loktevka River, Rudnyi Altai, Altaiskii Krai, Western Siberia, Russia.[2]

Crystallography

Aurichalcite displays prismatic crystals often in the form of encrustations and sometimes columnar structures.[4] The crystal system is monoclinic.

References
  1. Handbook of Mineralogy
  2. Mindat
  3. Webmineral data
  4. "Aurichalcite Mineral Data." https://www.mindat.org/min-422.html Accessed 18 February 2019.
Display at the Arizona-Sonora Desert Museum
Aurichalcite in gossan
Needle Crystals of Aurichalcite from Nevada, USA
Clear Smithsonite over blue Aurichalcite from Kelly Mine, Soccorro co., New Mexico
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