Botryoidal malachite. 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 amorphous (non-crystalline) form. Malachite is most often formed by precipitation from hydrothermal fluids in open spaces (voids) of rocks containing or associated with copper ores. Such precipitation takes place layer by layer, as with stalactites, ending up as grape-like (botryoidal) or kidney-like masses. Malachite is famous for its vivid green colour and is extensively worked into trinkets and all kind of small ornaments. This specimen is from the Congolese copper-mining province Shaba, actual height 180 mm.