Malachite

Malachite is a basic copper carbonate, Cu₂CO₃(OH)₂. It forms in the oxidation zones of copper deposits, mostly as green botryoidal crusts, stalactites and banded masses, also as silky sprays of fine needles; distinct crystals are rare. Where azurite takes up water and loses carbon dioxide, it turns into malachite and keeps its crystal shape, and these pseudomorphs are a subject of their own for collectors. The main source today is Katanga in the DR Congo, with its copper mines around Kolwezi, Likasi and Kambove. Collectors also know malachite from Tsumeb in Namibia, from Bisbee and Ray in Arizona, and from the Urals, whose mines supplied the stone for the Malachite Room of the Winter Palace in St. Petersburg.