Aurichalcite

View more Science videos

Environment

Secondary (gossan) zone of copper zinc ore deposits.

Crystals never well defined, usually in delicate crusts of thin, fragile scales.

Pale greenish blue. Luster pearly; hardness 2; specific gravity 3.5-3.6; cleavage micaceous. Flexible; translucent.

A basic carbonate of zinc and copper (20.8% CuO, 53.2% ZnO, 16.1% CO ₂ , 9.9% H ₂ O).

Infusible on charcoal but colors the flame green. Soluble in hydrochloric acid with effervescence, giving green solution, which turns blue on the addition of ammonia.

The soft pale blue-green scales, which dissolve so easily in acid, are unlike those of any other mineral. A limonite gossan occurrence is also usual.

Since aurichalcite forms as a result of weathering in ore bodies rather high in zinc, it is a good guide to zinc ore; less conspicuous when copper predominates. Usually forms soft crusts on limonite, often with calcite, smithsonite, and hemimorphite. It is a minor zinc source when smelted with other minerals.

Good specimens have come from several localities in Utah, and it is also found in some of the Arizona, New Mexico, and Mexican copper mines. European localities include the Leadhills locality, Scotland, famous for rare oxide zone minerals; Matlock in Derbyshire; the Altai region of Russia; former Yugoslavia; and Chessy, France.

The origin of the name evokes interest, as it is derived from the ancient name for brass (an alloy of copper and zinc). In truth, the mineral can be considered a natural "brass ore," though it is quantitatively so rare that it is unlikely it ever served this purpose.

Aurichalcite
Aurichalcite, 79 Mine, Banner District, Gila County, Arizona, USA
General
Category	Carbonate mineral
Chemical formula	(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

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

1. ^ ^{a b} Handbook of Mineralogy
2. ^ ^{a b c} Mindat
3. ^ Webmineral data

Display at the Arizona-Sonora Desert Museum

Aurichalcite in gossan

Needle Crystals of Aurichalcite from Nevada, USA

Wikimedia Commons has media related to: Aurichalcite

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)