- a very common mineral, iron oxide, Fe2O3, occurring in steel-gray to black crystals and in red earthy masses: the principal ore of iron.
- a red, grey, or black mineral, found as massive beds and in veins and igneous rocks. It is the chief source of iron. Composition: iron (ferric) oxide. Formula: Fe 2 O 3 . Crystal structure: hexagonal (rhombohedral)
