Cobaltite

Cobaltite is a sulfide mineral composed of cobalt, arsenic and sulfur, CoAsS. It contains up to 10 percent 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.