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Magnetite is a mineral and one of the main , with the chemical formula . It is one of the iron oxide, and is ferrimagnetism; (2025). 9780444519795, Elsevier Science. ISBN 9780444519795 it is attracted to a magnet and can be magnetization to become a permanent magnet itself. With the exception of extremely rare native iron deposits, it is the most magnetic of all the naturally occurring minerals on Earth. Naturally magnetized pieces of magnetite, called lodestone, will attract small pieces of iron, which is how ancient peoples first discovered the property of magnetism.
Magnetite is black or brownish-black with a metallic luster, has a Mohs hardness of 5–6 and leaves a black streak. Small grains of magnetite are very common in igneous rocks and metamorphic rocks. (2025). 9780195106916, Oxford University Press. ISBN 9780195106916
The chemical IUPAC name is iron(II,III) oxide and the common chemical name is ferrous-ferric oxide.
As a member of the inverse spinel group, magnetite can form with similarly structured minerals, including ulvospinel () and magnesioferrite ().
Titanomagnetite, also known as titaniferous magnetite, is a solid solution between magnetite and ulvospinel that crystallizes in many mafic igneous rocks. Titanomagnetite may undergo oxy-exsolution during cooling, resulting in ingrowths of magnetite and ilmenite.
Hydrothermal synthesis usually produces single octahedral crystals which can be as large as across. In the presence of mineralizers such as 0.1M HI or 2M NH4Cl and at 0.207MPa at 416–800 °C, magnetite grew as crystals whose shapes were a combination of rhombic-dodechahedra forms. The crystals were more rounded than usual. The appearance of higher forms was considered as a result from a decrease in the surface energies caused by the lower surface to volume ratio in the rounded crystals.
Commonly, contain solid solutions of both titanomagnetite and hemoilmenite or titanohematite. Compositions of the mineral pairs are used to calculate oxygen fugacity: a range of oxidizing conditions are found in magmas and the oxidation state helps to determine how the magmas might evolve by fractional crystallization. (1984). 9780198578109, Freeman, Cooper. ISBN 9780198578109 Magnetite also is produced from and by serpentinite. (1989). 9780582300965, Longman Scientific & Technical. ISBN 9780582300965
The relationships between magnetite and other iron oxide minerals such as ilmenite, hematite, and ulvospinel have been much studied; the reactions between these minerals and oxygen influence how and when magnetite preserves a record of the Earth's magnetic field. (2025). 9780520260313, University of California Press. ISBN 9780520260313
At low temperatures, magnetite undergoes a crystal structure phase transition from a monoclinic structure to a cubic structure known as the Verwey transition. Optical studies show that this metal to insulator transition is sharp and occurs around 120K. The Verwey transition is dependent on grain size, domain state, pressure, and the iron-oxygen stoichiometry. An isotropic point also occurs near the Verwey transition around 130K, at which point the sign of the magnetocrystalline anisotropy constant changes from positive to negative. The Curie temperature of magnetite is .
If magnetite is in a large enough quantity it can be found in aeromagnetic surveys using a magnetometer which measures magnetic intensities.
Large deposits of magnetite are also found in the Atacama region of Chile (Chilean Iron Belt); the Valentines region of Uruguay; Kiruna, Sweden; the Tallawang region of New South Wales; and in the Adirondack Mountains of New York in the United States. Kediet ej Jill, the highest mountain of Mauritania, is made entirely of the mineral. European Space Agency, esa.int (access: August 2, 2020) In the municipalities of Molinaseca, Albares, and Rabanal del Camino, in the province of León (Spain), there is a magnetite deposit in Ordovician terrain, considered one of the largest in Europe. It was exploited between 1955 and 1982.Miguel Calvo Rebollar (2025). 9788495063991, Escuela Técnica Superior de Ingenieros de Minas de Madrid. Fundación Gómez Pardo. ISBN 9788495063991 Deposits are also found in Norway, Romania, and Ukraine. Magnetite-rich sand dunes are found in southern Peru. In 2005, an exploration company, Cardero Resources, discovered a vast deposit of magnetite-bearing sand dunes in Peru. The dune field covers 250 square kilometers (100 sq mi), with the highest dune at over 2,000 meters (6,560 ft) above the desert floor. The sand contains 10% magnetite.
In large enough quantities magnetite can affect compass navigation. In Tasmania there are many areas with highly magnetized rocks that can greatly influence compasses. Extra steps and repeated observations are required when using a compass in Tasmania to keep navigation problems to the minimum.
Magnetite crystals with a cube habit are rare but have been found at Balmat, St. Lawrence County, New York, and at Långban, Sweden. This habit may be a result of crystallization in the presence of cations such as zinc.
Magnetite can also be found in due to biomineralization and are referred to as . There are also instances of magnetite with origins in Outer space coming from .
]]Pure magnetite particles are biomineralized in , which are produced by several species of magnetotactic bacteria. Magnetosomes consist of long chains of oriented magnetite particles that are used by bacteria for navigation. After the death of these bacteria, the magnetite particles in magnetosomes may be preserved in sediments as magnetofossils. Some types of anaerobic bacteria that are not magnetotactic can also create magnetite in oxygen free sediments by reducing amorphic ferric oxide to magnetite.
Several species of birds are known to incorporate magnetite crystals in the upper beak for magnetoreception, which (in conjunction with cryptochromes in the retina) gives them the ability to sense the direction, polarity, and magnitude of the ambient magnetic field.
Chitons, a type of mollusk, have a tongue-like structure known as a radula, covered with magnetite-coated teeth, or denticles. The hardness of the magnetite helps in breaking down food.
Biological magnetite may store information about the magnetic fields the organism was exposed to, potentially allowing scientists to learn about the migration of the organism or about changes in the Earth's magnetic field over time.
Some researchers also suggest that humans possess a magnetic sense, proposing that this could allow certain people to use magnetoreception for navigation. The role of magnetite in the brain is still not well understood, and there has been a general lag in applying more modern, interdisciplinary techniques to the study of biomagnetism.
Electron microscope scans of human brain-tissue samples are able to differentiate between magnetite produced by the body's own cells and magnetite absorbed from airborne pollution, the natural forms being jagged and crystalline, while magnetite pollution occurs as rounded . Potentially a human health hazard, airborne magnetite is a result of pollution (specifically combustion). These nanoparticles can travel to the brain via the olfactory nerve, increasing the concentration of magnetite in the brain. In some brain samples, the nanoparticle pollution outnumbers the natural particles by as much as 100:1, and such pollution-borne magnetite particles may be linked to abnormal neural deterioration. In one study, the characteristic nanoparticles were found in the brains of 37 people: 29 of these, aged 3 to 85, had lived and died in Mexico City, a significant air pollution hotspot. Some of the further eight, aged 62 to 92, from Manchester, England, had died with varying severities of neurodegenerative diseases. Such particles could conceivably contribute to diseases like Alzheimer's disease. Though a causal link has not yet been established, laboratory studies suggest that iron oxides such as magnetite are a component of Senile plaques in the brain. Such plaques have been linked to Alzheimer's disease.
Increased iron levels, specifically magnetic iron, have been found in portions of the brain in Alzheimer's patients. Monitoring changes in iron concentrations may make it possible to detect the loss of neurons and the development of neurodegenerative diseases prior to the onset of symptoms due to the relationship between magnetite and ferritin. In tissue, magnetite and ferritin can produce small magnetic fields which will interact with magnetic resonance imaging (MRI) creating contrast. Huntington patients have not shown increased magnetite levels; however, high levels have been found in study mice.
Another application of magnetic nanoparticles is in the creation of . These are used in several ways. Ferrofluids can be used for targeted drug delivery in the human body. The magnetization of the particles bound with drug molecules allows "magnetic dragging" of the solution to the desired area of the body. This would allow the treatment of only a small area of the body, rather than the body as a whole, and could be highly useful in cancer treatment, among other things. Ferrofluids are also used in magnetic resonance imaging (MRI) technology.
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