Hematite, also spelled as haematite, is a common iron oxide with a formula of Fe₂O₃ and is widespread in rocks and soils. Hematite forms in the shape of crystals through the rhombohedral lattice system, and it has the same crystal structure as ilmenite and corundum. Hematite and ilmenite form a complete solid solution at temperatures above 950 °C.
Hematite is colored black to steel or silver-gray, brown to reddish-brown, or red. It is mined as the main ore of iron. Varieties include kidney ore, martite, iron rose and specularite. While these forms vary, they all have a rust-red streak. Hematite is harder than pure iron, but much more brittle. Maghemite is a hematite- and magnetite-related oxide mineral.
Large deposits of hematite are found in banded iron formations. Gray hematite is typically found in places that can have still, standing water or mineral hot springs, such as those in Yellowstone National Park in North America. The mineral can precipitate out of water and collect in layers at the bottom of a lake, spring, or other standing water. Hematite can also occur without water, usually as the result of volcanic activity.