Magnetite is one of the very few minerals that isferrimagnetic; it is attracted by amagnet as shown hereUnit cell of magnetite. The gray spheres are oxygen, green are divalent iron, blue are trivalent iron. Also shown are an iron atom in an octahedral space (light blue) and another in a tetrahedral space (gray).
Magnetite is amineral and one of the mainiron ores, with the chemical formulaFe2+Fe3+2O4. It is one of theoxides of iron, and isferrimagnetic;[6] it is attracted to amagnet and can bemagnetized to become a permanent magnet itself.[7][8] With the exception of extremely rarenative iron deposits, it is the most magnetic of all the naturally occurring minerals on Earth.[7][9] Naturally magnetized pieces of magnetite, calledlodestone, will attract small pieces of iron, which is how ancient peoples first discovered the property of magnetism.[10]
In addition to igneous rocks, magnetite also occurs insedimentary rocks, includingbanded iron formations and in lake and marine sediments as both detrital grains and asmagnetofossils. Magnetite nanoparticles are also thought to form in soils, where they probably oxidize rapidly tomaghemite.[13]
The chemical composition of magnetite is Fe2+(Fe3+)2(O2-)4. This indicates that magnetite contains bothferrous (divalent) andferric (trivalent) iron, suggesting crystallization in an environment containing intermediate levels of oxygen.[14][15] The main details of its structure were established in 1915. It was one of the first crystal structures to be obtained usingX-ray diffraction. The structure is inversespinel, with O2- ions forming aface-centered cubic lattice and iron cations occupyinginterstitial sites. Half of the Fe3+ cations occupy tetrahedral sites while the other half, along with Fe2+ cations, occupy octahedral sites. The unit cell consists of thirty-twoO2- ions and unit cell length isa = 0.839 nm.[15][16]
Titanomagnetite, also known as titaniferous magnetite, is a solid solution between magnetite and ulvospinel that crystallizes in manymafic igneous rocks. Titanomagnetite may undergooxy-exsolution during cooling, resulting in ingrowths of magnetite and ilmenite.[17]
Natural and synthetic magnetite occurs most commonly asoctahedral crystals bounded by {111} planes and asrhombic-dodecahedra.[15] Twinning occurs on the {111} plane.[3]
Hydrothermal synthesis usually produces single octahedral crystals which can be as large as 10 mm (0.39 in) across.[15] In the presence of mineralizers such as 0.1M HI or 2MNH4Cl and at 0.207MPa at 416–800 °C, magnetite grew as crystals whose shapes were a combination of rhombic-dodechahedra forms.[15] 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.[15]
Magnetite has been important in understanding the conditions under which rocks form. Magnetite reacts with oxygen to producehematite, and the mineral pair forms abuffer that can control how oxidizing its environment is (theoxygenfugacity). This buffer is known as the hematite-magnetite or HM buffer. At lower oxygen levels, magnetite can form a buffer withquartz andfayalite known as the QFM buffer. At still lower oxygen levels, magnetite forms a buffer withwüstite known as the MW buffer. The QFM and MW buffers have been used extensively in laboratory experiments on rock chemistry. The QFM buffer, in particular, produces an oxygen fugacity close to that of most igneous rocks.[18][19]
Commonly,igneous rocks contain solid solutions of both titanomagnetite and hemoilmenite or titanohematite. Compositions of the mineral pairs are used to calculate oxygen fugacity: a range ofoxidizing conditions are found in magmas and the oxidation state helps to determine how the magmas might evolve byfractional crystallization.[20] Magnetite also is produced fromperidotites anddunites byserpentinization.[21]
The relationships between magnetite and other iron oxide minerals such asilmenite, hematite, andulvospinel have been much studied; thereactions between these minerals and oxygen influence how and when magnetite preserves a record of theEarth's magnetic field.[23]
At low temperatures, magnetite undergoes a crystal structurephase transition from a monoclinic structure to a cubic structure known as theVerwey transition. Optical studies show that this metal to insulator transition is sharp and occurs around 120K.[24] The Verwey transition is dependent on grain size, domain state, pressure,[25] and the iron-oxygenstoichiometry.[26] 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.[27] TheCurie temperature of magnetite is 580 °C (853 K; 1,076 °F).[28]
Magnetite is sometimes found in large quantities in beach sand. Suchblack sands (mineral sands oriron sands) are found in various places, such asLung Kwu Tan in Hong Kong;California, United States; and the west coast of theNorth Island of New Zealand.[32] The magnetite, eroded from rocks, is carried to the beach by rivers and concentrated by wave action and currents. Huge deposits have been found in banded iron formations.[33][34] These sedimentary rocks have been used to infer changes in the oxygen content of the atmosphere of the Earth.[35]
Large deposits of magnetite are also found in theAtacama region of Chile (Chilean Iron Belt);[36] theValentines region of Uruguay;[37]Kiruna, Sweden;[38] theTallawang region of New South Wales;[39] and in theAdirondack Mountains ofNew York in the United States.[40]Kediet ej Jill, the highest mountain ofMauritania, is made entirely of the mineral.[41] 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.[42] Deposits are also found inNorway,Romania, andUkraine.[43] Magnetite-rich sand dunes are found in southern Peru.[44] In 2005, an exploration company, Cardero Resources, discovered a vast deposit of magnetite-bearing sand dunes inPeru. 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.[45]
In large enough quantities magnetite can affectcompassnavigation. InTasmania 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.[46]
Biomagnetism is usually related to the presence of biogenic crystals of magnetite, which occur widely in organisms.[53] These organisms range frommagnetotactic bacteria (e.g.,Magnetospirillum magnetotacticum) to animals, including humans, where magnetite crystals (and other magnetically sensitive compounds) are found in different organs, depending on the species.[54][55] Biomagnetites account for the effects of weak magnetic fields on biological systems.[56] There is also a chemical basis for cellular sensitivity to electric and magnetic fields (galvanotaxis).[57]
Pure magnetite particles arebiomineralized inmagnetosomes, which are produced by several species ofmagnetotactic bacteria. Magnetosomes consist of long chains of oriented magnetite particle 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 ofanaerobic bacteria that are not magnetotactic can also create magnetite in oxygen free sediments by reducing amorphic ferric oxide to magnetite.[58]
Chitons, a type of mollusk, have a tongue-like structure known as aradula, covered with magnetite-coated teeth, ordenticles.[61] 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.[62]
Living organisms can produce magnetite.[55] In humans, magnetite can be found in various parts of the brain including thefrontal,parietal,occipital, andtemporal lobes,brainstem,cerebellum andbasal ganglia.[55][63] Iron can be found in three forms in the brain – magnetite, hemoglobin (blood) andferritin (protein), and areas of the brain related tomotor function generally contain more iron.[63][64] Magnetite can be found in thehippocampus. The hippocampus is associated with information processing, specifically learning and memory.[63] However, magnetite can have toxic effects due to its charge or magnetic nature and its involvement in oxidative stress or the production offree radicals.[65] Research suggests thatbeta-amyloid plaques andtau proteins associated withneurodegenerative disease frequently occur after oxidative stress and the build-up of iron.[63]
Some researchers also suggest that humans possess a magnetic sense,[66] proposing that this could allow certain people to use magnetoreception for navigation.[67] 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.[68]
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 roundednanoparticles. 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.[63][65] 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.[69] Such particles could conceivably contribute to diseases likeAlzheimer's disease.[70] Though a causal link has not yet been established, laboratory studies suggest that iron oxides such as magnetite are a component ofprotein plaques in the brain. Such plaques have been linked toAlzheimer's disease.[71]
Increased iron levels, specifically magnetic iron, have been found in portions of the brain in Alzheimer's patients.[72] 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[64][72] due to the relationship between magnetite andferritin.[63] In tissue, magnetite and ferritin can produce small magnetic fields which will interact withmagnetic resonance imaging (MRI) creating contrast.[72] Huntington patients have not shown increased magnetite levels; however, high levels have been found in study mice.[63]
Audio recording using magnetic acetate tape was developed in the 1930s. The Germanmagnetophon first utilized magnetite powder that BASF coated onto cellulose acetate before soon switching to gamma ferric oxide for its superior morphology.[75] FollowingWorld War II,3M Company continued work on the German design. In 1946, the 3M researchers found they could also improve their own magnetite-based paper tape, which utilized powders of cubic crystals, by replacing the magnetite with needle-shaped particles ofgamma ferric oxide (γ-Fe2O3).[75]
Approximately 2–3% of the world's energy budget is allocated to theHaber Process for nitrogen fixation, which relies on magnetite-derived catalysts. The industrial catalyst is obtained from finely ground iron powder, which is usually obtained by reduction of high-purity magnetite. The pulverized iron metal is burnt (oxidized) to give magnetite or wüstite of a defined particle size. The magnetite (or wüstite) particles are then partially reduced, removing some of theoxygen in the process. The resulting catalyst particles consist of a core of magnetite, encased in a shell of wüstite, which in turn is surrounded by an outer shell of iron metal. The catalyst maintains most of its bulk volume during the reduction, resulting in a highly porous high-surface-area material, which enhances its effectiveness as a catalyst.[76][77]
Magnetite micro- and nanoparticles are used in a variety of applications, from biomedical to environmental. One use is in water purification: in high gradient magnetic separation, magnetite nanoparticles introduced into contaminated water will bind to the suspended particles (solids, bacteria, or plankton, for example) and settle to the bottom of the fluid, allowing the contaminants to be removed and the magnetite particles to be recycled and reused.[78] This method works with radioactive and carcinogenic particles as well, making it an important cleanup tool in the case of heavy metals introduced into water systems.[79]
Another application of magnetic nanoparticles is in the creation offerrofluids. These are used in several ways. Ferrofluids can be used for targeteddrug delivery in the human body.[78] 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 inmagnetic resonance imaging (MRI) technology.[80]
For theseparation of coal from waste, dense medium baths were used. This technique employed the difference in densities betweencoal (1.3–1.4 tonnes per m3) and shales (2.2–2.4 tonnes per m3). In a medium with intermediatedensity (water with magnetite), stones sank and coal floated.[81]
^Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W."Magnetite"(PDF).Handbook of Mineralogy. Chantilly, VA: Mineralogical Society of America. p. 333. Retrieved15 November 2018.
^ab"Magnetite". mindat.org and the Hudson Institute of Mineralogy. Retrieved15 November 2018.
^Barthelmy, Dave."Magnetite Mineral Data".Mineralogy Database. webmineral.com. Retrieved15 November 2018.
^Jacobsen, S.D.; Reichmann, H.J.; Kantor, A.; Spetzler, H.A. (2005). "A gigahertz ultrasonic interferometer for the diamond anvil cell and high-pressure elasticity of some iron-oxide minerals". In Chen, J.; Duffy, T.S.; Dobrzhinetskaya, L.F.; Wang, Y.; Shen, G. (eds.).Advances in High-Pressure Technology for Geophysical Applications. Elsevier Science. pp. 25–48.doi:10.1016/B978-044451979-5.50004-1.ISBN978-0-444-51979-5.
^Nesse, William D. (2000).Introduction to mineralogy. New York: Oxford University Press. p. 361.ISBN9780195106916.
^Morel, Mauricio; Martínez, Francisco; Mosquera, Edgar (October 2013). "Synthesis and characterization of magnetite nanoparticles from mineral magnetite".Journal of Magnetism and Magnetic Materials.343:76–81.Bibcode:2013JMMM..343...76M.doi:10.1016/j.jmmm.2013.04.075.
^Kesler, Stephen E.; Simon, Adam F. (2015).Mineral resources, economics and the environment (2nd ed.). Cambridge, United Kingdom: Cambridge University Press.ISBN9781107074910.OCLC907621860.
^Carmichael, Ian S.E.; Ghiorso, Mark S. (June 1986). "Oxidation-reduction relations in basic magma: a case for homogeneous equilibria".Earth and Planetary Science Letters.78 (2–3):200–210.Bibcode:1986E&PSL..78..200C.doi:10.1016/0012-821X(86)90061-0.
^Philpotts, Anthony R.; Ague, Jay J. (2009).Principles of igneous and metamorphic petrology (2nd ed.). Cambridge, UK: Cambridge University Press. pp. 261–265.ISBN9780521880060.
^McBirney, Alexander R. (1984).Igneous petrology. San Francisco, Calif.: Freeman, Cooper. pp. 125–127.ISBN0198578105.
^Yardley, B. W. D. (1989).An introduction to metamorphic petrology. Harlow, Essex, England: Longman Scientific & Technical. p. 42.ISBN0582300967.
^Rasmussen, Birger; Muhling, Janet R. (March 2018). "Making magnetite late again: Evidence for widespread magnetite growth by thermal decomposition of siderite in Hamersley banded iron formations".Precambrian Research.306:64–93.Bibcode:2018PreR..306...64R.doi:10.1016/j.precamres.2017.12.017.
^Keyser, William; Ciobanu, Cristiana L.; Cook, Nigel J.; Wade, Benjamin P.; Kennedy, Allen; Kontonikas-Charos, Alkiviadis; Ehrig, Kathy; Feltus, Holly; Johnson, Geoff (February 2020). "Episodic mafic magmatism in the Eyre Peninsula: Defining syn- and post-depositional BIF environments for iron deposits in the Middleback Ranges, South Australia".Precambrian Research.337: 105535.Bibcode:2020PreR..33705535K.doi:10.1016/j.precamres.2019.105535.S2CID210264705.
^Klein, C. (1 October 2005). "Some Precambrian banded iron-formations (BIFs) from around the world: Their age, geologic setting, mineralogy, metamorphism, geochemistry, and origins".American Mineralogist.90 (10):1473–1499.Bibcode:2005AmMin..90.1473K.doi:10.2138/am.2005.1871.S2CID201124189.
^Knipping, Jaayke L.; Bilenker, Laura D.; Simon, Adam C.; Reich, Martin; Barra, Fernando; Deditius, Artur P.; Lundstrom, Craig; Bindeman, Ilya; Munizaga, Rodrigo (July 2015). "Giant Kiruna-type deposits form by efficient flotation of magmatic magnetite suspensions".Geology.43 (7):591–594.Bibcode:2015Geo....43..591K.doi:10.1130/G36650.1.hdl:10533/228146.
^Clark, David A. (September 2012). "Interpretation of the magnetic gradient tensor and normalized source strength applied to the Tallawang magnetite skarn deposit, New South Wales, Australia".SEG Technical Program Expanded Abstracts 2012:1–5.doi:10.1190/segam2012-0700.1.
^European Space Agency,esa.int (access: August 2, 2020)
^Calvo Rebollar, Miguel (2009).Minerales y Minas de España [Minerals and mines of Spain] (in Spanish). Vol. 4. Escuela Técnica Superior de Ingenieros de Minas de Madrid. Fundación Gómez Pardo. pp. 73–76.ISBN978-84-95063-99-1.
^Chamberlain, Steven C.; Robinson, George W.; Lupulescu, Marian; Morgan, Timothy C.; Johnson, John T.; deLorraine, William B. (May 2008). "Cubic and Tetrahexahedral Magnetite".Rocks & Minerals.83 (3):224–239.Bibcode:2008RoMin..83..224C.doi:10.3200/RMIN.83.3.224-239.S2CID129227218.
^Boström, Kurt (15 December 1972). "Magnetite Crystals of Cubic Habit from Långban, Sweden".Geologiska Föreningen i Stockholm Förhandlingar.94 (4):572–574.doi:10.1080/11035897209453690.
^abWiltschko, Roswitha; Wiltschko, Wolfgang (2014)."Sensing magnetic directions in birds: radical pair processes involving cryptochrome".Biosensors.4 (3):221–42.doi:10.3390/bios4030221.PMC4264356.PMID25587420.Birds can use the geomagnetic field for compass orientation. Behavioral experiments, mostly with migrating passerines, revealed three characteristics of the avian magnetic compass: (1) it works spontaneously only in a narrow functional window around the intensity of the ambient magnetic field, but can adapt to other intensities, (2) it is an "inclination compass", not based on the polarity of the magnetic field, but the axial course of the field lines, and (3) it requires short-wavelength light from UV to 565 nm Green.
^Kirschvink, J L; Kobayashi-Kirschvink, A; Diaz-Ricci, J C; Kirschvink, S J (1992). "Magnetite in human tissues: a mechanism for the biological effects of weak ELF magnetic fields".Bioelectromagnetics. Suppl 1:101–13.CiteSeerX10.1.1.326.4179.doi:10.1002/bem.2250130710.PMID1285705.A simple calculation shows that magnetosomes moving in response to earth-strength ELF fields are capable of opening trans-membrane ion channels, in a fashion similar to those predicted by ionic resonance models. Hence, the presence of trace levels of biogenic magnetite in virtually all human tissues examined suggests that similar biophysical processes may explain a variety of weak field ELF bioeffects.
^Lovley, Derek; Stolz, John; Nord, Gordon; Phillips, Elizabeth."Anaerobic production of magnetite by a dissimilatory iron-reducing microorganism"(PDF).geobacter.org. US Geological Survey, Reston, Virginia 22092, USA Department of Biochemistry, University of Massachusetts, Amherst, Massachusetts 01003, USA. Archived fromthe original(PDF) on 29 March 2017. Retrieved9 February 2018.
^Kishkinev, D A; Chernetsov, N S (2014). "[Magnetoreception systems in birds: a review of current research]".Zhurnal Obshcheĭ Biologii.75 (2):104–23.Bibcode:2015BioBR...5...46K.doi:10.1134/S2079086415010041.PMID25490840.There are good reasons to believe that this visual magnetoreceptor processes compass magnetic information which is necessary for migratory orientation.
^Lowenstam, H.A. (1967). "Lepidocrocite, an apatite mineral, and magnetic in teeth of chitons (Polyplacophora)".Science.156 (3780):1373–1375.Bibcode:1967Sci...156.1373L.doi:10.1126/science.156.3780.1373.PMID5610118.S2CID40567757.X-ray diffraction patterns show that the mature denticles of three extant chiton species are composed of the mineral lepidocrocite and an apatite mineral, probably francolite, in addition to magnetite.
^abcdefgMagnetite Nano-Particles in Information Processing: From the Bacteria to the Human Brain Neocortex -ISBN9781-61761-839-0
^abZecca, Luigi; Youdim, Moussa B. H.; Riederer, Peter; Connor, James R.; Crichton, Robert R. (2004). "Iron, brain ageing and neurodegenerative disorders".Nature Reviews Neuroscience.5 (11):863–873.doi:10.1038/nrn1537.PMID15496864.S2CID205500060.
^abcQin, Yuanyuan; Zhu, Wenzhen; Zhan, Chuanjia; Zhao, Lingyun; Wang, Jianzhi; Tian, Qing; Wang, Wei (August 2011). "Investigation on positive correlation of increased brain iron deposition with cognitive impairment in Alzheimer disease by using quantitative MR R2′ mapping".Journal of Huazhong University of Science and Technology [Medical Sciences].31 (4):578–585.doi:10.1007/s11596-011-0493-1.PMID21823025.S2CID21437342.
^Franz Oeters et al"Iron" in Ullmann's Encyclopedia of Industrial Chemistry, 2006, Wiley-VCH, Weinheim.doi:10.1002/14356007.a14_461.pub2
^Davis, E.W. (2004).Pioneering with taconite. Minnesota Historical Society Press.ISBN0873510232.
^Jozwiak, W. K.; Kaczmarek, E.; et al. (2007). "Reduction behavior of iron oxides in hydrogen and carbon monoxide atmospheres".Applied Catalysis A: General.326:17–27.doi:10.1016/j.apcata.2007.03.021.
^Rajput, Shalini; Pittman, Charles U.; Mohan, Dinesh (2016). "Magnetic magnetite (Fe 3 O 4 ) nanoparticle synthesis and applications for lead (Pb 2+ ) and chromium (Cr 6+ ) removal from water".Journal of Colloid and Interface Science.468:334–346.Bibcode:2016JCIS..468..334R.doi:10.1016/j.jcis.2015.12.008.PMID26859095.
