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Melanterite

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Melanterite
Melanterite as found in nature
General
CategorySulfate mineral
Formula
(repeating unit)
FeSO4·7H2O
IMA symbolMln[1]
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[2][3][4][5]

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[3] and as a rare sublimate phase around volcanic fumaroles.[5] Associated minerals include pisanite, chalcanthite, epsomite, pickeringite, halotrichite and other sulfate minerals.[5]

It was first described in 1850.[5]

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References

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  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ Mineralienatlas
  3. ^ a b Mindat
  4. ^ Webmineral data
  5. ^ a b c d Handbook of Mineralogy