A cubic mineral and member of the spinel structure type, space group Fd3m, with composition (Fe³⁺)^IV(Fe²⁺Fe³⁺)^VIO₄. It possesses the inverse spinel structure, in which half the ferric iron is tetrahedrally coordinated and the remaining half as well as all ferrous iron are octahedrally coordinated by the cubic close-packed oxygen atoms. The color is opaque iron-black and streak black, the hardness is 6 (Mohs scale), and the specific gravity is 5.20. The habit is octahedral (see illus.), but the mineral usually occurs in granular to massive form, sometimes of enormous dimensions. Though possessing no cleavage, some specimens show an octahedral parting. Limited Al³⁺ may substitute for Fe³⁺; and Ca²⁺, Mn²⁺, and Mg²⁺ for Fe²⁺.