Hematite (), also spelled as haematite, is a common iron oxide compound with the formula, Fe2O3 and is widely found in rocks and .
Hematite occurs naturally in black to steel or silver-gray, brown to reddish-brown, or red colors. It is Mining as an important ore mineral of iron. It is electrically conductive.
Large deposits of hematite are found in banded iron formations. Gray hematite is typically found in places that have still, standing water, or mineral , such as those in Yellowstone National Park in North America. The mineral may precipitate in the water and collect in layers at the bottom of the lake, spring, or other standing water. Hematite can also occur in the absence of water, usually as the result of Volcano activity.
Clay-sized hematite crystals also may occur as a secondary mineral formed by weathering processes in soil, and along with other iron oxides or such as goethite, which is responsible for the red color of many tropical, ancient, or otherwise highly weathered soils.
Etymology and history
The name hematite is derived from the
Greek language word for blood, αἷμα]]
(haima), due to the red coloration found in some varieties of hematite.
The color of hematite is often used as a
pigment. The English name of the stone is derived from
Middle French hématite pierre, which was taken from
Latin lapis haematites the 15th century, which originated from
Ancient Greek αἱματίτης λίθος (
haimatitēs lithos, "blood-red stone").
Ochre is a clay that is colored by varying amounts of hematite, varying between 20% and 70%.
Use of the red chalk of this iron-oxide mineral in writing, drawing, and decoration is among the earliest in human history. To date, the earliest known human use of the powdery mineral is 164,000 years ago by the inhabitants of the Pinnacle Point in what now is South Africa, possibly for social purposes.
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
spin canting 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 ). 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 spin canting 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.
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.
File:Hematite - Titanomagnitite.jpg|A microscopic picture of hematite
File:Hematite structure.jpg|Crystal structure of hematite
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.
is a pigment used in traditional Swedish house paints. It is made from tailings of the
Falun Mine.
Mars
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
are apparently
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.
Certain types of hematite- or iron-oxide-rich clay, especially
Armenian bole, have been used in
gilding. Hematite is also used in art such as in the creation of
Engraved gem.
Hematine is a synthetic material sold as
magnetic hematite.
Pigment
Hematite has been sourced to make
Pigment 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:Rutile-Hematite-113489.jpg|Golden acicular crystals of rutile radiating from a center of platy 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|Hematite, variant specularite (specular 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:Micaceous hematite.jpg|Mica hematite taken with permission from Kelly's Mine, Lustleigh, Devon UK
File:Hemacollage.png|Cumbria botryoidal hematite under Hand lens. Despite all being present on the same sample, the botryoids themselves vary widely in diameter.
See also
External links
