Aurichalcite

Aurichalcite
Aurichalcite, 79 Mine, Banner District, Gila County, Arizona, USA
General
Category	Carbonate mineral
Formula (repeating unit)	(Zn,Cu)5[(OH)3|CO3]2
Strunz classification	05.BA.15
Crystal symmetry	Monoclinic 2/m
Unit cell	a = 13.82 Å, b = 6.419 Å, 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
Crystal system	Monoclinic-prismatic
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

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.

Occurrence

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

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.

References

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Display at the Arizona-Sonora Desert Museum

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Aurichalcite in gossan

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Needle Crystals of Aurichalcite from Nevada, USA