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
Category	Carbonate mineral
Formula (repeating unit)	(Zn,Cu)5[(OH)3|CO3]2
Strunz classification	5.BA.15
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	P21/m
Unit cell	a = 13.82, b = 6.419 c = 5.29 [Å] β = 101.04°; Z = 2
Identification
Color	Pale green, greenish blue, sky-blue; colorless to pale blue, pale green in transmitted light
Crystal habit	Typically in tufted divergent sprays or spherical aggregates, may be in thick crusts; rarely columnar, laminated or granular
Twinning	Observed in X-ray patterns
Cleavage	{010} and {100} Perfect
Fracture	Uneven
Mohs scale hardness	2
Luster	Pearly, silky
Streak	Light blue
Diaphaneity	Transparent
Specific gravity	3.96
Optical properties	Biaxial (-)
Refractive index	nα = 1.655 nβ = 1.740 nγ = 1.744
Birefringence	0.0890
Pleochroism	Weak colorless to pale green
2V angle	Measured: 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.