Melanterite

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Melanterite
Melanterite2 - Copperas Mountain, Paxton Township, Ross Co, Ohio, USA.jpg
Melanterite as found in nature.
General
CategorySulfate mineral
Formula
(repeating unit)
FeSO4·7H2O
Strunz classification7.CB.35
Dana classification29.06.10.01
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupP21/c
Unit cella = 14.077 Å, b = 6.509 Å,
c = 11.054 Å; β = 105.6°; Z = 4
Identification
ColorGreen, pale green, greenish blue, bluish green, colorless
Crystal habitEncrustations and capillary efflorescences; rarely as equant pseudo-octahedral, prismatic or tabular crystals
Cleavage{001} Perfect, {110} Distinct
FractureConchoidal
Mohs scale hardness2
LusterVitreous
StreakWhite
DiaphaneitySubtransparent to translucent
Specific gravity1.89 - 1.9
Optical propertiesBiaxial (+)
Refractive indexnα = 1.470 - 1.471 nβ = 1.477 - 1.480 nγ = 1.486
References[1][2][3][4]

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[2] and as a rare sublimate phase around volcanic fumaroles.[4] Associated minerals include pisanite, chalcanthite, epsomite, pickeringite, halotrichite and other sulfate minerals.[4]

It was first described in 1850.[4]

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