Ferrimolybdite

Ferrimolybdite is a hydrous iron molybdate mineral with formula: Fe3+2(MoO4)3·8(H2O)[3] or Fe3+2(MoO4)3·n(H2O).[2] It forms coatings and radial aggregates of soft yellow needles which crystallize in the orthorhombic system.

Ferrimolybdite
Ferrimolybdite crystals from the Kingman District, Mohave County, Arizona
General
CategoryMolybdate mineral
Formula
(repeating unit)
Fe3+2(MoO4)3·8(H2O) or Fe3+2(MoO4)3·n(H2O)
IMA symbolFmyb[1]
Strunz classification7.GB.30
Crystal systemOrthorhombic
Crystal classDipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space groupPmmn
Unit cella = 6.665, b = 15.423
c = 29.901 [Å]; Z = 8
Identification
ColorCanary-yellow, straw-yellow, greenish yellow
Crystal habitAcicular tufted to radial aggregates; powdery, earthy
CleavageDistinct on {001}
FractureUneven
Mohs scale hardness1-2
LusterAdamantine, silky, earthy
StreakLight yellow
DiaphaneityTransparent to translucent
Specific gravity2.99
Optical propertiesBiaxial (+)
Refractive indexnα = 1.720 - 1.810 nβ = 1.730 - 1.830 nγ = 1.850 - 2.040
Birefringenceδ = 0.130 - 0.230
PleochroismX = Y = clear to nearly colorless; Z = dirty gray to canary-yellow
2V angle26° to 32° (calculated)
References[2][3][4]

Discovery and occurrence

It was first described in 1914 for an occurrence in the Alekseevskii Mine in the Karysh River Basin, Khakassia Republic, Siberia, Russia.[2] It was named for its composition (ferric iron and molybdenum).

It occurs as an oxidation product of molybdenum bearing ore deposits. Associated minerals include: molybdenite, pyrite and chalcopyrite.[3]

References

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