Chromite

Formula: Fe2+Cr2O4 multiple oxide, spinel group
Specific gravity: 4.5 to 4.8
Hardness: 5½
Streak: Brown
Colour: Brownish black to iron black
Solubility: Insoluble in hydrochloric, sulphuric and nitric acid
Environments:

Sedimentary environments
Placer deposits

Chromite is a common constituent of peridotite and other mafic rocks and of serpentine derived from them. It is one of the first minerals to separate from a cooling magma.

Alteration

Fe and Cr-rich spinel , diopside and enstatite to forsterite, anorthite and chromite
MgFeAl2Cr2O8 + CaMgSi2O6 + Mg2Si2O6 ⇌ 2Mg2SiO4 + Ca(Al2Si2O8) + Fe2+Cr2O4 This reaction occurs at fairly low temperature and pressure.

Common impurities: Mg,Mn,Zn,Al,Ti