Melanterite is a mineral form of hydrous iron(II) sulfate: FeSO4ยท7H2O. It is the iron analogue of the copper sulfate chalcanthite. It alters to siderotil by Dehydration. It is a secondary sulfate mineral which forms from the oxidation of primary such as pyrite and marcasite in the near-surface environment. It often occurs as a post mine encrustation on old underground mine surfaces. It also occurs in coal and lignite seams exposed to humid air[ and as a rare sublimate phase around volcanic .][ Associated minerals include pisanite, chalcanthite, epsomite, pickeringite, halotrichite and other sulfate minerals.][
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It was first described in 1850.[
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