Aurichalcite

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Aurichalcite
Aurichalcite-24456.jpg
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 [1][2][3]

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]

Occurrence[edit]

Auricalcite 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]

References[edit]

Aurichalcite in gossan
Needle Crystals of Aurichalcite from Nevada, USA