|Chemical formula||iron(III) oxide, Fe2O3, α-Fe2O3|
|Color||Metallic grey to earthy red|
|Crystal habit||Tabular to thick crystals|
|Crystal system||Hexagonal (rhombohedral)|
|Fracture||Uneven to sub-conchoidal|
|Mohs Scale hardness||5.5 - 6.5|
|Luster||Metallic to splendent|
|Streak||Bright red to dark red|
|Specific gravity||4.9 - 5.3|
Hematite (American English) or haematite (British English) is a common mineral that is mined as the principal ore of iron. Chemically, it corresponds to iron(III) oxide (Fe2O3), one of several iron oxides. It can be found in a range of colors, including black, silver-gray, and brown to reddish brown. The reddish brown color makes it suitable for use as a pigment. Polished, good quality hematite has an attractive appearance and is often used in jewelry.
Huge deposits of hematite are found in banded iron formations. Gray hematite is typically found in places where there has been standing water or mineral hot springs, such as those in Yellowstone. The mineral can precipitate out of water and collect in layers at the bottom of a lake, spring, or other standing water. But, hematite can also occur without water, as the result of volcanic activity.
Clay-sized hematite crystals can also occur as a secondary mineral formed by weathering processes in soil, and along with other iron oxides or oxyhydroxides such as goethite, is responsible for the red color of many tropical, ancient, or otherwise highly weathered soils.
Several varieties of hematite are known, including kidney ore, martite (pseudomorphs after magnetite), iron rose and specularite (specular hematite). While the forms of hematite vary, they all have a rust-red streak.
Hematite is harder than pure iron, but much more brittle. It crystallizes in the rhombohedral system, and it has the same crystal structure as ilmenite and as corundum. Hematite and ilmenite form a complete solid solution at temperatures above 950 °C.
Hematite is an antiferromagnetic material below 260 K (the Morin transition temperature); it is weakly ferromagnetic  between 260 K and 948 K (the Néel temperature); and it is paramagnetic above 948 K.
Hematite is part of a complex solid solution oxyhydoxide system having various degrees of water, hydroxyl group, and vacancy substitutions that affect the mineral's magnetic and crystal chemical properties. Two other end-members are referred to as protohematite and hydrohematite.
Hematite in popular culture
Polished hematite is considered by many to be a gemstone, and it has been used in jewelry over the last 50 years in North America, especially in the western United States. Its use in jewelry reached a height in Europe in Victorian times when it was very popular. Hematite can be found in jewelry and art created by the Native Americans.
- ↑ Hemoglobin is the oxygen-transporting molecule in red blood cells, the iron of which causes blood to be red.
- ↑ Ilmenite corresponds to a crystalline form of iron titanium oxide, FeTiO3.
- ↑ M.-Z. Dang, D. G. Rancourt, J. E. Dutrizac, G. Lamarche, and R. Provencher, "Interplay of Surface Conditions, Particle Size, Stoichiometry, Cell Parameters, and Magnetism in Synthetic Hematite-like Materials," Hyperfine Interactions 117 (1998): 271-319.
- Farndon, John. 2006. The Practical Encyclopedia of Rocks & Minerals: How to Find, Identify, Collect and Maintain the World's best Specimens, with over 1000 Photographs and Artworks. London: Lorenz Books. ISBN 0754815412 and ISBN 978-0754815419
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- Mindat.org. 2007. Hematite. Mindat.org. Retrieved March 21, 2007.
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