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.[3] Copper (Cu2+) gives aurichalcite its green-blue colors.[5]

For the fabulous metal, mentioned in the legend of the lost Atlantis, see Orichalcum.
Aurichalcite
General
CategoryCarbonate mineral
Formula
(repeating unit)		(Zn,Cu)5[(OH)3|CO3]2
IMA symbolAch[1]
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, light 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[2][3][4]

Occurrence

Aurichalcite typically occurs in the oxidized zone of copper and zinc deposits. Associated minerals include: rosasite, smithsonite, hemimorphite, hydrozincite, malachite and azurite.[2]

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 orichalcum, a fabulous metal, mentioned in the legend of the mythic lost continent Atlantis. The type locality is the Loktevskoye Mine, Upper Loktevka River, Rudnyi Altai, Altaiskii Krai, Western Siberia, Russia.[3]

Crystallography

Aurichalcite displays prismatic crystals often in the form of encrustations and sometimes columnar structures.[6] The crystal system is monoclinic.

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. Handbook of Mineralogy
  3. Mindat
  4. Webmineral data
  5. "Minerals Colored by Metal Ions". minerals.gps.caltech.edu. Retrieved 2023-03-01.
  6. "Aurichalcite Mineral Data." https://www.mindat.org/min-422.html Accessed 18 February 2019.
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