Cobaltite is a sulfide mineral composed of cobalt, arsenic, and sulfur, CoAsS. Its impurities may contain up to 10% iron and variable amounts of nickel. Structurally, it resembles pyrite (FeS2) with one of the sulfur atoms replaced by an arsenic atom.
Although rare, it is mined as a significant source of the strategically important metal cobalt. Secondary weathering incrustations of erythrite, hydrated cobalt arsenate, are common.[citation needed] A variety containing much iron replacing cobalt, and known as ferrocobaltite (German: Stahlkobalt), was found at Siegen in Westphalia.
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