It forms by the reaction of metallic cobalt, its oxide, hydroxide, or carbonate with aqueous sulfuric acid:[1] The heptahydrate is only stable at humidity >70% at room temperature, otherwise it converts to the hexahydrate.

[1] The hexahydrate is a metal aquo complex consisting of octahedral [Co(H2O)6]2+ ions associated with sulfate anions (see image in table).

Thus, crushed, partially refined ores are treated with sulfuric acid to give red-colored solutions containing cobalt sulfate.

Cobalt(II) sulfate is used in storage batteries and electroplating baths, sympathetic inks, and as an additive to soils and animal feeds.

[1] Being commonly available commercially, the heptahydrate is a routine source of cobalt in coordination chemistry.