Magnesiochromite Locality: Mistake Mine (Butler Estate Mine; Mistaken; Big Ridge & Mistake Mine; James-Thickston; James-Thickstun Mine), Butler Estate Chrome deposit, Wright Mountain, New Idria District, Diablo Range, Fresno Co., California, USA A 3.2 by 2.5 cms mass of rough crystals. JSS specimen and photo — Photo: John Sobolewski (JSS) · CC BY 3.0
Magnesiochromite
The magnesium end-member of the chromite spinel series — MgCr₂O₄.
Intro adapted from Wikipedia (CC BY-SA).
Magnesiochromite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula MgCr₂O₄.
It crystallizes in the cubic crystal system (space group Fd-3m). It is a member of the Spinel structural group.
Key properties: Mohs hardness 5.5–7; specific gravity 4.39–4.67; Brown streak; Metallic luster.
IMA symbol Mchr, grandfathered status — known before the IMA’s founding, named in 1873.
An accessory mineral in ultramafic rocks, as dunites, serpentinites, kimberlites, lamproites, and komatiites. More rarely as xenocrysts in lamprophyres and mid-ocean basalts. May be detrital.
It is found associated with Olivine, augite, magnetite, plagioclase, pigeonite.
The name refers to a MAGNESIum-rich chromite.