Formula: MgCr2O4
Multiple oxide, spinel subgroup, forms a complete series with chromite and with spinel


Picrochromite is a variety of magnesiochromite

Specific gravity: 4.2
Hardness: 5½
Streak: Brown
Colour: Black
Common impurities: Fe,Al

Igneous environments
Metamorphic environments

Magnesiochromite occurs as an accessory mineral in ultramafic rocks, such as dunite, serpentinite and kimberlite. More rarely it is found as xenocrysts in lamprophyre and mid-ocean basalt. It may be detrital. Associated minerals include olivine, augite, magnetite, plagioclase and pigeonite (HOM).


At the type locality, the Schwarzenberg mining district, Erzgebirgskreis, Saxony, Germany, magnesiochromite occurs in serpentinite (Dana).

At Dun Mountain, Nelson Region, New Zealand, magnesiochromite occurs in dunite (Dana).

At the Clear Creek District, Kern county, California, USA, ferroan magnesiochromite is common both as masses and as octagonal crystals in the serpentinite. Many of the grains have been fractures and filled with cinnabar. Hydrothermal fluids have altered the magnesiochromite to eskolaite, which, on further reduction, provided the chromate that formed the mercury-bearing chromates (Minrec 36.4.354).

At the Cripple Creek Mining District, Teller county, Colorado, USA, magnesiochromite has been reported as inclusions in olivine in monchiquite, phonolitic-tephrite and tephritic phonolite (Minrec 36.2.173).

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