Ferrimolybdite

Ferrimolybdite

Yellow sprays of ferrimolybdite on quartz from the Liège Province, Belgium
General
Category Molybdate mineral
Formula
(repeating unit)
Fe3+2(MoO4)3·8(H2O) or Fe3+2(MoO4)3·n(H2O)
Strunz classification 7.GB.30
Crystal symmetry Orthorhombic dipyramidal
H-M symbol: mmm
Space group: Pmmn
Unit cell a = 6.665 Å, b = 15.423 Å, c = 29.901 Å; Z=8
Identification
Color Canary-yellow, straw-yellow, greenish yellow
Crystal habit Acicular tufted to radial aggregates; powdery, earthy
Crystal system Orthorombic
Cleavage Distinct on {001}
Fracture Uneven
Mohs scale hardness 1-2
Luster Adamantine, silky, earthy
Streak Light yellow
Diaphaneity Transparent to translucent
Specific gravity 2.99
Optical properties Biaxial (+)
Refractive index nα = 1.720 - 1.810 nβ = 1.730 - 1.830 nγ = 1.850 - 2.040
Birefringence δ = 0.130 - 0.230
Pleochroism X = Y = clear to nearly colorless; Z = dirty gray to canary-yellow
2V angle 26° to 32° (calculated)
References [1][2][3]

Ferrimolybdite is a hydrous iron molybdate mineral with formula: Fe3+2(MoO4)3·8(H2O)[2] or Fe3+2(MoO4)3·n(H2O).[1] It forms coatings and radial aggregates of soft yellow needles which crystallize in the orthorhombic system.

Ferrimolybdite crystals from the Kingman District, Mohave County, Arizona

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.[1] 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.[2]

References

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