Melanterite
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Melanterite is a mineral form of hydrous iron sulfate: FeSO4·7H2O. It is the iron analogue of the copper sulfate chalcanthite. It alters to siderotil by loss of water. It is a secondary sulfate minera
Melanterite as found in nature
Cuprian melanterite
Pickeringite
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Pickeringite is a magnesium aluminium sulfate mineral with formula MgAl24·22. It forms a series with halotrichite.
Cobalt rich pickeringite from the Northern Slanské Mts, Prešov Region, Slovakia
Pickeringite in the Natural History Museum