Melanterite

(repeating unit)FeSO₄·7H₂OIMA symbolMln^[1]Strunz classification7.CB.35Dana classification29.06.10.01Crystal systemMonoclinicCrystal classPrismatic (2/m)
(same H-M symbol)Space groupP2₁/cUnit cella = 14.077 Å, b = 6.509 Å,
c = 11.054 Å; β = 105.6°; Z = 4IdentificationColorGreen, pale green, greenish blue, bluish green, colorlessCrystal habitEncrustations and capillary efflorescences; rarely as equant pseudo-octahedral, prismatic or tabular crystalsCleavage{001} Perfect, {110} DistinctFractureConchoidalMohs scale hardness2LusterVitreousStreakWhiteDiaphaneitySubtransparent to translucentSpecific gravity1.89 – 1.9Optical propertiesBiaxial (+)Refractive indexnα = 1.470 – 1.471 nβ = 1.477 – 1.480 nγ = 1.486References^[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]

Gallery

• 
  Crystal structure of melanterite
• 
  Cuprian melanterite

References