Member of the garnet group of minerals, Fe₃Al₂(SiO₄)₃; sp. gr. 4.25; hardness 6.5–7.5; cubic; red, brown-red, or black; greasy to vitreous lustre; most common crystals are dodecahedra, and many are irregular grains; widely distributed in metamorphic and igneous rocks, and in beach sands and placers. Transparent crystals are used as gemstones, and the mineral is useful in general as an abrasive.