Cobaltite is a mineral composed of cobalt, iron, arsenic sulfide, (Co,Fe)AsS. Structuraly 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.
It is found chiefly in Sweden, Norway, India, and Azerbaijan.