Magnesioferrite
(repeating unit)Mg(Fe3+)2O4 IMA symbol Mfr[1] 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 [2][3][4] 
H-M symbol: (4/m 3 2/m)
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.
Occurrence
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.[2]
It has been reported from Vesuvius and Stromboli, Italy.
References
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