Magnesioferrite Dimensions: 9.5 cm x 6 cm x 5 cm; weight: 650g Locality: Långban, Filipstad, Värmland, Sweden — Photo: Omer Vanheule · Public domain
Magnesioferrite
A black magnesium-iron spinel forming metallic octahedra — named simply for magnesium plus ferric iron.
Intro adapted from Wikipedia (CC BY-SA).
Magnesioferrite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula MgFe³⁺₂O₄.
It crystallizes in the cubic crystal system (space group Fd3m). It is a member of the Spinel structural group.
Key properties: Mohs hardness 6–6.5; specific gravity 4.55–4.65; Black streak; Metallic to semimetallic, may be dull luster; refractive index 2.38; optically isotropic.
IMA symbol Mfr, grandfathered status — known before the IMA’s founding, named in 1859.
Most commonly of fumarolic origin; also in high-grade (sanidinite facies) combustion-metamorphosed marls and burning coal heaps; in metamorphosed dolostones. An accessory mineral in some kimberlites, carbonatites, and alkali gabbros.
It is found associated with Hematite, titanian magnetite, ferrian diopside.
The name comes from the composition, with dominant MAGNESium and FERRic iron.