Hematite

Hematite, also spelled hæmatite, is the solid solution at temperatures above 950°C.  

Hematite is a very common 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 (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 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.

The name hematite is derived from the Greek word for blood (haima) because hematite can be red, as in pigment.  

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

Magnetism

Hematite is an paramagnetic.  

The magnetic structure of a-hematite was the subject of considerable discussion and debate in the 1950s because it appeared to be ferromagnetic with a Curie temperature of around 1000 K, but with an extremely tiny moment (0.002mB). Adding to the surprise was a transition with a decrease in temperature at around 260 K to a phase with no net magnetic moment.^{[citation needed]}

Dzialoshinksi and later Moriya showed that the system is essentially antiferromagnetic but that the low symmetry of the cation sites allows spin–orbit coupling to cause canting of the moments when they are in the plane perpendicular to the c axis. The disappearance of the moment with a decrease in temperature at 260 K is caused by a change in the anisotropy which causes the moments to align along the c axis. In this configuration, spin canting does not reduce the energy.^{[citation needed]}

Hematite is part of a complex solid solution oxyhydroxide system having various degrees of water, hydroxyl group, and vacancy substitutions that affect the mineral's magnetic and crystal chemical properties.^[3] 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 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