Hematite

Hematite - Titanomagnitite

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Hematite structure

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Hematite-LTH43A

Quartz-Hematite-113680

Hematite, also spelled as haematite, is an iron oxide compound with the formula Fe2O3 and is one of several iron oxides. It is the oldest known iron oxide mineral that has ever formed on earth, and is widespread in rocks and soils. Hematite crystallizes in 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 (pseudomorphs after magnetite), iron rose and specularite (specular hematite). 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, however, usually as the result of volcanic activity.

Uses

Hematite is used in a variety of applications, from pigments to radiation shielding. Its use as a pigment has been prevalent since ancient times in the form of red ochre. Hematite is also used in art for creating intaglio engraved gems. Beyond its aesthetic uses, hematite is of significant industrial value. It is a key ore of iron, which is used to produce steel, a fundamental material in construction and manufacturing. Additionally, hematite is utilized in the production of magnets (when magnetized), jewelry, and other decorative items. Its properties also make it useful for radiation shielding and heavy media separation.

Formation and Locations

Hematite forms by both inorganic and organic processes. On Earth, it can form through the oxidation of iron minerals in the presence of water, a process that occurs in the soil, in lake and ocean beds, and in volcanic regions. One of the most common ways hematite forms is through a chemical reaction in highly oxidizing environments.

Significant hematite deposits can be found in countries such as Australia, Brazil, Canada, India, Russia, South Africa, and the United States, making it widely available across the globe. The largest hematite ore deposits are typically found in banded iron formations which are extensive layers of sedimentary rock composed of alternating layers of iron-rich minerals and silica (or quartz).

Cultural and Historical Significance

Historically, hematite has played a significant role in human culture as a pigment (red ochre) and as a symbol of blood and warfare. Its use dates back to prehistoric times, and it has been discovered in burial sites and ancient art around the world. In some cultures, hematite was used to create amulets believed to protect against bleeding or to give the wearer strength.

Physical and Chemical Properties

Hematite is a relatively dense mineral, with a specific gravity ranging from 4.9 to 5.3. Its Mohs hardness is around 5.5 to 6.5, making it somewhat hard but also brittle. The mineral is typically steel gray to black in appearance, but it can also show a range of reds, browns, and reds when powdered or in certain lighting conditions. Hematite's streak is typically red to reddish-brown, which is one of its distinguishing characteristics.

Environmental and Health Considerations

While hematite is not considered hazardous, fine dust and particles generated during the mining and processing of hematite can pose health risks if inhaled. Workers in industries dealing with hematite should use appropriate protective equipment to avoid respiratory issues.