Ferrimolybdite

Ferrimolybdite
240px 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

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

File:Ferrimolybdite-154908.jpg

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. 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.