The mineral malachite is a hydrated copper carbonate with chemical formula Cu2CO3(OH)2. It crystallizes in the monoclinic crystal system, and usually occurs in massive form, 'botryoidal' (grape-like) or 'kidney-shaped' on the outside, and internally banded. It also occurs, more rarely, as stalactites. Malachite is usually formed by precipitation from fluids around or associated with copper ores. It is famous for its vivid green colours and extensively worked into trinkets and other small ornaments.This specimen is from the Congolese copper-mining province Shaba and measures about 20 cm across.