Cobaltite is a sulfide mineral compound of cobalt, arsenic, and sulfur, Its chemical formula is CoAsS. It contains 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, known as "Cobalt bloom," are common; erythrite is a pink to crimson hydrated cobalt arsenate mineral.