Atacamite,

Atacamite, an ore of copper, found in the iron-mines of Schwartzenberg in Saxony, and also as a crust on the lavas of Vesuvius and Etna, especially on those of Vesuvius erupted in the years 97, 1804, 1820, and 1822. It occurs abundantly in some parts of South America, as in Atacama, from which it derives its name, and other districts in Chili; and at Tarapaca (now also Chilian) it is associated in veins with ores of silver. The natural varieties of atacamite are crystallised, massive, and pulverulent or granular. The massive or compact variety is usually reniform, with a fibrous structure. The crystals are short and needle-shaped; the primary form is a rhombic prism or rectangular octahedron. It has been sometimes described as a chloride of copper, but incorrectly; and sometimes as a hydrochlorate (muriate) of copper: it is rather to be regarded as a combination of protoxide of copper with chloride of copper. It is a rich and productive ore, containing about 55 to 60 per cent. of copper. Atacamite often forms on the surface of copper exposed to the air or sea-water; and the greenish incrustation observed on antique bronze utensils, weapons, and other articles, and commonly known as the verugo nobilis, is composed of this salt. On some antique bronzes from Egypt the atacamite is crystalline. Atacamite is worked in South America as an ore of copper; and considerable quantities are sent to England to have the metal extracted therefrom. See COPPER.