Bixbyite

Bixbyite
Bixbyite from Utah
General
Category	Oxide minerals
Formula (repeating unit)	(Mn,Fe)2O3
Strunz classification	4.CB.10
Dana classification	4.3.7.2
Crystal system	Isometric
Crystal class	Diploidal (m3) H-M symbol: (2/m 3)
Space group	Ia3
Unit cell	a = 9.411 Å; Z = 16
Identification
Formula mass	158.33 g/mol
Color	Black
Crystal habit	Massive to crystalline
Twinning	On {111}, as penetration twins
Cleavage	Imperfect on {111}, in traces
Fracture	Irregular to uneven
Mohs scale hardness	6 - 6½
Luster	Metallic
Streak	Black
Diaphaneity	Opaque
Specific gravity	5.12
Density	4.95
Optical properties	Isotropic
Common impurities	Al, Mg, Si, Ti
References

Bixbyite is a manganese iron oxide mineral with chemical formula: (Mn,Fe)₂O₃. The iron/manganese ratio is quite variable and many specimens have almost no iron. It is a metallic dark black with a Mohs hardness of 6.0 - 6.5. It is a somewhat rare mineral sought after by collectors as it typically forms euhedral isometric crystals exhibiting various cubes, octahedra, and dodecahedra.

It is commonly associated with beryl, quartz, spessartine, hematite, pseudobrookite, hausmannite, braunite and topaz in pneumatolytic or hydrothermal veins and cavities and in metamorphic rocks. It can also be found in lithophysal cavities in rhyolite. Typical localities are Jhabua and Chhindwara districts, India and the Thomas Range in Juab County, Utah. It is also reported from San Luis Potosi, Mexico; northern Patagonia, Argentina; Girona, Catalonia, Spain; Sweden and South Africa.