Melanterite and chalcanthite, 70 mm, Filizchai field, Balaken region, Azerbaijan — Photo: IbrZulya · CC BY-SA 4.0
Melanterite
Hydrated iron(II) sulfate — the green 'copperas' that crusts oxidizing pyrite deposits; the iron analogue of chalcanthite.
Intro adapted from Wikipedia (CC BY-SA).
Melanterite is an IMA-recognized mineral species in the sulfate class, with the chemical formula Fe(SO₄)·7H₂O.
It crystallizes in the monoclinic crystal system (space group P2_1/c). It is a member of the Melanterite structural group.
Key properties: Mohs hardness 2; specific gravity 1.9; typically green or yellow; White streak; Vitreous luster; refractive index 1.477; optically biaxial.
IMA symbol Mln, grandfathered status — known before the IMA’s founding.
A post-mine product of oxidation of pyrite and marcasite ores; rarely a volcanic sublimate.
It is found associated with Pisanite, chalcanthite, epsomite, pickeringite, halotrichite, other sulfates.
Its name comes from the Greek for a black metallic dye.
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