Hematite

The name hematite is derived from the Greek word for blood, (haima), due to the red coloration found in some varieties of hematite. 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. Hematite residues are also found in graves from 80,000 years ago. Near Rydno in Poland and Lovas in Hungary red chalk mines have been found that are from 5000 BC, belonging to the Linear Pottery culture at the Upper Rhine. Rich deposits of hematite have been found on the island of Elba that have been mined since the time of the Etruscans. Underground hematite mining is classified as a carcinogenic hazard to humans. ==Magnetism==

Hematite shows only a very feeble response to a magnetic field. Unlike magnetite, it is not noticeably attracted to an ordinary magnet. Hematite is an antiferromagnetic material below the Morin transition at , and a canted antiferromagnet or weakly ferromagnetic above the Morin transition and below its Néel temperature at , above which it is paramagnetic. The magnetic structure of α-hematite was the subject of considerable discussion and debate during the 1950s, as it appeared to be ferromagnetic with a Curie temperature of approximately , but with an extremely small magnetic moment (0.002 Bohr magnetons). Adding to the surprise was a transition with a decrease in temperature at around to a phase with no net magnetic moment. It was shown 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 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. The magnetic properties of bulk hematite differ from their nanoscale counterparts. For example, the Morin transition temperature of hematite decreases with a decrease in the particle size. The suppression of this transition has been observed in hematite nanoparticles and is attributed to the presence of impurities, water molecules and defects in the crystals lattice. Hematite is part of a complex solid solution oxyhydroxide system having various contents of H2O (water), hydroxyl groups and vacancy substitutions that affect the mineral's magnetic and crystal chemical properties. Two other end-members are referred to as protohematite and hydrohematite. Enhanced magnetic coercivities for hematite have been achieved by dry-heating a two-line ferrihydrite precursor prepared from solution. Hematite exhibited temperature-dependent magnetic coercivity values ranging from . The origin of these high coercivity values has been interpreted as a consequence of the subparticle structure induced by the different particle and crystallite size growth rates at increasing annealing temperature. These differences in the growth rates are translated into a progressive development of a subparticle structure at the nanoscale (super small). At lower temperatures (350–600 °C), single particles crystallize. However, at higher temperatures (600–1000 °C), the growth of crystalline aggregates, and a subparticle structure is favored. ==Mine tailings==

Hematite is present in the waste tailings of iron mines. A recently developed process, magnetation, uses magnets to glean waste hematite from old mine tailings in Minnesota's vast Mesabi Range iron district. Falu red is a pigment used in traditional Swedish house paints. It is made from tailings of the Falun Mine. ==Mars==

partly embedded in rock at the Opportunity landing site. Image is around across. The spectral signature of hematite was seen on the planet Mars by the infrared spectrometer on the NASA Mars Global Surveyor 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 Aram Chaos site near the Valles Marineris. Several other sites also showed hematite, such as 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 sent 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 "Martian spherules" that were informally named "blueberries" by the science team. Analysis indicates that these spherules are apparently concretions formed from a water solution. "Knowing just how the hematite on Mars was formed will help us characterize the past environment and determine whether that environment was favorable for life". ==Jewelry==

Hematite is often shaped into beads, tumbling stones, and other jewellery components. Hematite was once used as mourning jewelry. == Pigment ==

Hematite has been sourced to make pigments since earlier origins of human pictorial depictions, such as on cave linings and other surfaces, and has been employed continually in artwork through the eras. In Roman times, the pigment obtained by finely grinding hematite was known as sil atticum. Other names for the mineral when used in painting include colcotar and caput mortuum. In Spanish, it is called almagre or almagra, from the Arabic al-maghrah, red earth, which passed into English and Portuguese. Other ancient names for the pigment include ochra hispanica, sil atticum antiquorum, and Spanish brown. It forms the basis for red, purple, and brown iron-oxide pigments, as well as being an important component of ochre, sienna, and umber pigments. The main producer of hematite for the pigment industry is India, followed distantly by Spain. == Industrial purposes ==

As mentioned earlier, hematite is an important mineral for iron ore. The physical properties of hematite are also employed in the areas of medical equipment, shipping industries, and coal production. Having high density and capable as an effective barrier against X-ray passage, it often is incorporated into radiation shielding. As with other iron ores, it often is a component of ship ballasts because of its density and economy. In the coal industry, it can be formed into a high specific density solution, to help separate coal powder from impurities. ==Gallery==

File:Hematite-LTH43A.JPG|A rare pseudo-scalenohedral crystal habit File:Quartz-Hematite-113680.jpg|Three gemmy quartz crystals containing bright rust-red inclusions of hematite, on a field of sparkly black specular hematite File:Cylinder seal antelope Louvre AM1639.jpg|Cypro-Minoan cylinder seal (left) made from hematite with corresponding impression (right), approximately 14th century BC File:Hematite-254990.jpg|A cluster of parallel-growth, mirror-bright, metallic-gray hematite blades from Brazil File:Hematite.bear.660pix.jpg|Hematite carving, long File:Hematit 2.jpg|Specularite (specular hematite) variety of hematite, with fine grain shown File:Hematite-rich BIF ventifact.jpg|Red hematite from a banded iron formation in Wyoming File:Hematite on mars.jpg|Hematite on Mars as found in form of "blueberries" (named by NASA) File:Hematite streak plate.jpg|Streak plate, showing that hematite consistently leaves a rust-red streak File:Hematite in Scanning Electron Microscope, magnification 100x.JPG|Hematite in scanning electron microscope, magnification 100x File:Hemacollage.png|Cumbrian botryoidal hematite under hand-lens. Despite all being present on the same sample, the botryoids themselves vary widely in diameter. File:Hematite (GeoDIL number - 1382).jpg|Hematite kidney ore ==See also==