Copiapite

Copiapite is a hydrated iron sulfate mineral with formula: FeFe₄(SO₄)₆(OH)₂·20(H₂O). Copiapite can also refer to a mineral group, the copiapite group.

Copiapite is strictly a secondary mineral forming from the weathering or oxidation of iron sulfide minerals or sulfide-rich coal. Its most common occurrence is as the end member mineral from the rapid oxidation of pyrite. It also occurs rarely with fumaroles. It occurs with melanterite, alunogen, fibroferrite, halotrichite, botryogen, butlerite and amarantite. It is by far the most common mineral in the copiapite group.