Bixbyite

Bixbyite
General
Category	Oxide minerals
Formula (repeating unit)	(Mn,Fe)2O3
IMA symbol	Bxb[1]
Strunz classification	4.CB.10
Dana classification	4.3.7.2
Crystal system	Cubic
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 – 6+1⁄2
Luster	Metallic
Streak	Black
Diaphaneity	Opaque
Specific gravity	5.12
Density	4.95
Optical properties	Isotropic
Refractive index	2.51 – 2.56
Common impurities	Al, Mg, Si, Ti
References	[2][3][4][5]

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.^[3] 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.^[3] 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, Germany, Namibia, Zimbabwe, and South Africa.^[3][6]

Bixbyite was named for the American mineralogist Maynard Bixby (1853–1935), responsible for its discovery in 1897.^[3] It should not be confused with bixbite, a red form of beryl; to avoid confusion, this name has been deprecated from the CIBJO and the IMA.