haematite n : the principal form of iron ore; consists of ferric oxide in crystalline form; occurs in a red earthy form [syn: hematite]

English

Alternative spellings

• hæmatite (old-fashioned), hematite (US)

Noun

1. In the context of "chiefly UK": An iron ore, mainly peroxide of iron.

Hematite, also spelled hæmatite, is the mineral form of Iron(III) oxide (Fe2O3), one of several iron oxides. Hematite 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 a mineral, 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 the forms of hematite vary, they all have a rust-red streak. Hematite is harder than pure iron, but much more brittle.

Huge deposits of hematite are found in banded iron formations. Grey 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. Hematite can also occur without water, however, usually 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.

Good specimens of hematite come from England, Mexico, Brazil, Australia and the Lake Superior region of the United States and Canada.

Ochre

The name hematite is derived from the Greek word for blood (haima) because hematite can be red, as in rouge, a powdered form of hematite. The color of hematite lends it well in use as a pigment.

Ochre is a clay that is colored by varying amounts of hematite, varying between 20% and 70% . Red ochre contains unhydrated hematite, whereas yellow ochre contains hydrated hematite (Fe2O3 • H2O). The principal use of ochre is for tinting with a permanent color Two other end-members are referred to as protohematite and hydrohematite.

Hematite on Mars

The spectral signature of hematite was seen on the planet Mars by the infrared spectrometer on the NASA Mars Global Surveyor ("MGS") and 2001 Mars Odyssey spacecraft in orbit around Mars . The mineral was seen in abundance at two sites. on the planet, the Terra Meridiani site, near the Martian equator at 0° longitude, and the second site Aram Chaos near the Valles Marineris . Several other sites also showed hematite, e.g., Aureum Chaos . Because terrestrial hematite is typically a mineral formed in aqueous environments, or by aqueous alteration, this detection was scientifically interesting enough that the second of the two Mars Exploration Rovers was targeted to a site in the Terra Meridiani region designated Meridiani Planum. In-situ investigations by the Opportunity rover showed a significant amount of hematite, much of it in the form of small spherules that were informally tagged by the science team "blueberries" (a term which is somewhat confusing, since in spectrally-correct color images they are, in fact, silver-grey in color). Analysis indicates that these spherules are apparently concretions formed from a water solution.

Jewelry

Hematite's popularity in jewelry was at its highest in Europe during the Victorian era, while in the last 50 years it has been popular in North America, especially in the western United States where it is found in jewelry and art created by Native Americans. Care should be taken in handling hematite items due to the material's susceptibility to damage.

See also

• Iron ore
• List of minerals
• Wüstite
• Magnetite
• Mineral redox buffer
• Scientific information from the Mars Exploration Rover mission

References

• Martite - Mindat w/ location data
• Iron rose - Mindat w/ locations

External links

• Abandoned Mine Research.
• Mars spheres image.
• Mars trench image showing a shiny texture of half-buried spheres (dark line is equipment shadow)
• Florence Mine, Cumbria, UK.
• MineralData.org