Magnesioferrite

magnesioferrite

diopside

dolomite

bromellite

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Formula: MgFe³⁺₂O₄
Multiple oxide, spinel subgroup, forms a series with magnetite
Crystal System: Isometric
Specific gravity: 4.56 to 4.65 measured, 4.51 calculated
Hardness: 6 to 6½
Streak: Black or dark red
Colour: Black, reddish-brown in transmitted light
Environments:

Metamorphic environments
Fumeroles
Coal-seam fires

Magnesioferrite is most commonly found in fumeroles where it probably formed by the reaction at high temperature of steam and ferric chloride with magnesian material (Dana). It is also found in sanidinite facies combustion-metamorphosed marl and burning coal heaps, and in metamorphosed dolostone (HOM). It is an accessory mineral in some kimberlite, gabbro and carbonatites (HOM).
Magnesioferrite is associated with hematite, titanium-rich magnetite, iron-rich diopside and dolomite, and at Långban, Sweden, occasionally with bromellite (Dana).

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