25 Photos
Melanterite
Chemical Formula	FeSO4·7H2O
Species	Sulfates
Crystal System	Monoclinic
Mohs Scale	2
Specific Gravity	1.89-1.9
Color	Green, pale green, greenish blue, bluish green, colorless
Streak	White
Luster	Vitreous
Refractive Index	n = 1.470 - 1.471 n = 1.477 - 1.480 n = 1.486
Diaphaneity	Translucent, Opaque
Cleavage	PerfectPerfect on , distinct on .
Fracture	Conchoidal
Crystal Habit：Encrustations and capillary efflorescences; rarely as equant pseudo-octahedral, prismatic or tabular crystals
Geological Setting：A secondary mineral formed by the oxidation of iron sulfide minerals, such as pyrite and marcasite, it is found occurring naturally in sheltered crevices and cavities in sulfidic sedimentary and metamorphic rocks, and in coal and lignite deposits. It also forms readily on the walls, timbers, and other structures in mines.

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 post mine encrustation on old underground mine surfaces. It also occurs in coal and lignite seams exposed to humid air. It also occurs as a rare sublimate phase around volcanic fumaroles. Associated minerals include pisanite, chalcanthite, epsomite, pickeringite, halotrichite and other sulfate minerals.

It was first described in 1850.