Hematite, also spelled as hæmatite,'s the mineral form of Iron(III) oxide (Fe2O3), one of several iron oxides. Hematite crystallizes in the rhombohedral system, and it's the same crystal structure as ilmenite and as corundum. Hematite and ilmenite form a complete solid solution at temperatures above 950°C. Hematite's a mineral, colored black to steel or silver-gray, brown to reddish brown, or red. It's mined as the main ore of iron. Varieties include kidney ore, martite (pseudomorphs… (More on Hematite)