Member of the garnet group of minerals, that has the formula Mn3 Al2 (SiO4)3; sp. gr. 4.18; hardness 6.5–7.5; cubic; dark red to orange-yellow or brown; greasy to vitreous lustre; crystals commonly dodecahedra; widely distributed in metamorphic and igneous rocks, and in beach and river sands. It is named after the Spessart Mountains, Bavaria, Germany.