atacamite

(mineralogy) Cu₂Cl(OH)₃ Native, green hydrouscopper oxychloride crystallizing in the orthorhombic system.

Environment

Weathered, secondary ore deposits in arid climates.

Usually in thin to substantial (1-in., 1-3 cm) prisms. Sometimes in tabular form, when it resembles brochantite or antlerite; also fibrous, massive, granular, and as sand.

Deep emerald green. Luster glassy; hardness 3-3Ɖ; specific gravity 3.8; streak green; fracture conchoidal; cleavage side pinacoid. Brittle, transparent.

Basic copper chloride (74.3% Cu, 13.0% Cl, 12.7% H ₂ O).

Fuses easily, giving continuously a bright blue flame like that normally seen briefly after a touch of hydrochloric acid. Will finally yield copper bead. Easily soluble to a green solution in nitric acid and gives chlorine test (with silver nitrate), leaving a blue solution above the white precipitate.

Resembles malachite (but while dissolving does not effervesce) and some copper phosphates and sulfates (which do not so readily--nor for so long--give the blue copper flame without hydrochloric acid, nor do they give a chlorine test).

A rare copper mineral of wholly secondary origin; results from the alteration, through weathering and usually under desert conditions, of copper sulfide minerals. Common under the extreme conditions of continuous dryness of the South American west coast in Chile (the Atacama Desert). The best crystals, nevertheless, came from South Australia. Small needles have been recorded at Vesuvius in a fumarole deposit. The U.S. has produced a few examples at several western localities--including San Manuel, Arizona--but it is probably often unrecognized, being confused with similar-appearing and more common minerals such as brochantite and malachite. Among the popular species sought by competitive collectors, good examples are likely to be high-priced.

In South America it is a significant ore when mined with other copper-bearing minerals. Once fashionably elegant as a sand for ink-drying (before blotters); the supplies for this were commonly imported by the British from Chile.

Atacamite.

Atacamite is a mineral found originally in the desert of Atacama Desert, Chile, and named by D. de Gallizen in 1801. It is a copper(II) chloride hydroxide, with formula Cu₂Cl(OH)₃.

Its colour is various shades of green, usually dark. Atacamite is a comparatively rare mineral, formed from primary copper minerals in the oxidation or weathering zone of arid climates.

External links

• Mineral galleries
• Mindat

References

• This article incorporates text from the Encyclopædia Britannica Eleventh Edition, a publication now in the public domain.

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