Magnesioferrite

Magnesioferrite
Magnesioferrite from Ochtendung, Eifel, Germany
General
Category	Oxide minerals Spinel group Spinel structural group
Formula (repeating unit)	Mg(Fe3+)2O4
Strunz classification	4.BB.05
Crystal system	Cubic
Crystal class	Hexoctahedral (m3m) H-M symbol: (4/m 3 2/m)
Space group	Fd3m
Unit cell	a = 8.3866 Å; Z = 8
Identification
Color	Black to brownish black
Crystal habit	As octahedral crystals, massive granular
Twinning	Twin plane {111}, contact twins
Cleavage	On {111}
Fracture	Uneven
Tenacity	Brittle
Mohs scale hardness	6 - 6.5
Luster	Metallic, semimetallic, dull
Streak	Dark red
Diaphaneity	Opaque, transparent in thin fragments
Specific gravity	4.55 – 4.65 measured
Optical properties	Isotropic
Refractive index	n = 2.38
Other characteristics	Magnetic
References

Magnesioferrite is a magnesium iron oxide mineral, a member of the magnetite series of spinels. Magnesioferrite crystallizes as black metallic octahedral crystals. It is named after its chemical composition of magnesium and ferric iron. The density is 4.6 - 4.7 (average = 4.65), and the diaphaniety is opaque. Occurs as well-formed fine sized crystals or massive and granular. Its hardness is 6-6.5. It has a metallic luster and a dark red streak.

It occurs in fumaroles, as a result of combustion metamorphism and coal seam fires, in glass spherules related to meteorite impacts, and as accessory phase in kimberlites and carbonatites.

It has been reported from Vesuvius and Stromboli, Italy.