1) Monoclinic mineral 
Melanterite is a mineral form of hydrous iron(II) 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 mineral which forms from the oxidation of primary sulfide minerals such as pyrite and marcasite in the near-surface environment. It often occurs as a ...
• (n.) A hydrous sulphate of iron of a green color and vitreous luster; iron vitriol.
Me·lan'ter·ite noun (Min.) A hydrous sulphate of iron of a green color and vitreous luster; iron vitriol. 
Melanterite is a hydrous sulphate of iron of a green colour and vitreous lustre.
Iron(II) sulfate