Rozenite

Rozenite is an uncommon hydrous iron sulfate mineral, FeSO₄•4(H₂O).

It occurs as a secondary mineral, formed under low humidity at less than 21 °C (70 °F) as an alteration of copper-free melanterite which is a post mine alteration product of pyrite or marcasite. It also occurs in lacustrine sediments and coal seams. Associated minerals include melanterite, epsomite, jarosite, gypsum, sulfur, pyrite, marcasite and limonite.