Properties of Hematite
Hematite (AE) or haematite (BE) (sometimes miss-spelled as hemitite) is the mineral form of Iron (III) oxide, (Fe2O3), one of several iron oxides, formed from Magnetite. Magnetite is the most magnetic of all the naturally occurring minerals on Earth, and these magnetic properties led to its use as an early form of magnetic compass. Magnetite reacts with oxygen to produce hematite, and the mineral pair forms a buffer that can control oxygen fugacity. Hematite also has the same crystal structure as ilmenite and corundum. Hematite is one of the most naturally occurring earth magnets with very special magnetic properties.
Color properties of Hematite
Hematite (kidney ore) from Michigan Hematite is a very common mineral, colored black to steel or silver-gray, brown to reddish brown, or red. Varieties include kidney ore, martite (pseudo-morphs 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.
Formation properties of Hematite
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 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 oxy-hydroxides such as goethite, is responsible for the red color of many tropical, ancient, or otherwise highly weathered soils.
The History of Hematite
The name hematite is derived from the Greek word for blood (haima), since sometimes hematite can be red, as in Rouge, a powdered form of hematite. It shares this root with the word hemoglobin. Hemoglobin is the oxygen-transporting molecule in red blood cells, the iron of which causes blood to be red. The color of hematite lends it well in use as a pigment. As mentioned earlier various forms of hematite were used as early compasses.
Magnetic Properties of Hematite
Hematite is an antiferromagnetic material at normal living temperatures. In materials that exhibit anti-ferro-magnetism, the spins of electrons align in a regular pattern with neighboring spins pointing in opposite directions. This is a very different manifestation of magnetism that sets hematite apart from many other magnets used for bio-magnetic therapy.
Scientific Magnetic Properties of Hematite
Hematite is an antiferromagnetic material below the Morin transition at 260K, and a canted antiferromagnet or weakly ferromagnetic  above the Morin transition and below its Néel temperature at 948K, above which it is paramagnetic. Generally, antiferromagnetic materials exhibit antiferromagnetism at a low temperature, and become disordered above a certain temperature; the transition temperature is called the Néel temperature. Above the Néel temperature, the material is typically paramagnetic.
Bio-magnetic Properties of Hematite for Humans
Hematite and its close relative’s lodestone (magnetite) grow in bacteria. This bio-magnetic bacterium is called magneto-tactic bacteria. There is no chemically sensible reason why bacteria would have favored this compound of iron over all others unless the magnetic properties of this element were important, or useful, in some way. Biologists think that organisms may use these as bio-magnetic internal compasses to sense where 'down' is so that they can find food.
In 1974, R. Blakemore at the University of New Hampshire uncovered that certain species of fresh water bacteria creates within their single-celled bodies nearly two-dozen pure cubical crystals of magnetite as they grow. Like pearls on a string, these magnetic crystals are oriented along the axis of the bacterium. By some evolutionary process primitive organisms somehow grew a single crystal of magnetite, perhaps as a byproduct of ingestion. As these crystals accumulated in the host, it became more efficient in finding its way to new locations rather than being lost in the dark. It is considered that these lowly bacteria managed to discover a bio-magnetic compass about 3 billion years ago. (Ref = Sci Am, 245, p. 58 1981)
Using these magnetic clues, scientists have examined many different organisms under the microscope, and many have been found to have some form of magnetite embedded in them. Results indicate bio-magnetic materials are found in homing pigeons, tuna, honey bees, dolphins, whales and green turtles. It is well known that homing-pigeon rallies are note held during times when geo-magnetic conditions are not stable.
But how does an organism 'sense' which direction magnetite crystals are pointing inside them? How do you know which way? The most telling examples seem to be found in mammals. In 1982 an article in Science magazine called "Magnetic Navigation, an Attractive Possibility', by Maugh (Science 215, 1492.) explains how microscopic examination of the magnetite crystals turned up some forms of "nervous tissue". A book by Kirchvink, Jones and Mac Fadden was written on "Magnetite Biomineralization and Magnetoreception in Organisms (Plennum Press, NY, 1985).
Further, in 1983 Baker, Mather and Kennaugh of the University of Manchester discovered "Magnetic bones in human sinuses" as documented in their Science journal article (301, p. 78). These are where the considerations for hematite as a magnetic equalizer and stabilizer have been considered science. Humans may be able to support their bio-magnetic balancing act with the help of hematite magnets as magnetic compasses that balance our central nervous system and support the healing process.
The magnetic qualities and beauty of hematite have made it a natural bio-magnetic substance for magnetic therapy jewelry, including magnetic hematite bracelets and magnetic hematite necklaces.
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