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Magnetite
""Magnetite-118736.jpg
Magnetite from Bolivia
General
Category
"Formula
(repeating unit)
iron(II,III) oxide, Fe2+Fe3+2O4
"Strunz classification 4.BB.05
"Crystal system "Isometric
"Crystal class Hexoctahedral (m3m)
"H-M symbol: (4/m 3 2/m)
"Space group Fd3m
"Unit cell a = 8.397 Å; Z = 8
Identification
Color Black, gray with brownish tint in reflected sun
"Crystal habit "Octahedral, fine granular to massive
"Twinning On {Ill} as both twin and composition plane, the spinel law, as contact twins
"Cleavage Indistinct, parting on {Ill}, very good
"Fracture Uneven
"Tenacity Brittle
"Mohs scale hardness 5.5–6.5
"Luster Metallic
"Streak Black
"Diaphaneity Opaque
"Specific gravity 5.17–5.18
"Solubility Dissolves slowly in "hydrochloric acid
References [1][2][3][4]
Major varieties
"Lodestone Magnetic with definite north and south poles

Magnetite is a "mineral and one of the main iron ores. With the chemical formula "Fe3O4, it is one of the "oxides of iron. Magnetite is "ferrimagnetic; it is attracted to a "magnet and can be "magnetized to become a "permanent magnet itself.[5][6] It is the most "magnetic of all the naturally-occurring minerals on Earth.[5][7] Naturally-magnetized pieces of magnetite, called "lodestone, will attract small pieces of iron, which is how ancient peoples first discovered the property of "magnetism. Today it is mined as "iron ore.

Small grains of magnetite occur in almost all "igneous and "metamorphic rocks. Magnetite is black or brownish-black with a metallic luster, has a "Mohs hardness of 5–6 and leaves a black "streak.[5]

The chemical "IUPAC name is "iron(II,III) oxide and the common chemical name is ferrous-ferric oxide.

Contents

Properties[edit]

In addition to igneous rocks, magnetite also occurs in "sedimentary rocks, including "banded iron formations and in lake and marine sediments as both detrital grains and as "magnetofossils. Magnetite nanoparticles are also thought to form in soils, where they probably oxidize rapidly to "maghemite.[8]

Crystal structure[edit]

The chemical composition of magnetite is Fe2+Fe23+O42−. The main details of its structure were established in 1915 one of the first obtained using "X-ray diffraction. The structure is inverse "spinel, with O2- ions forming a "face centered cubic lattice and iron cations occupying interstitial 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 32 O2- ions and unit cell length is a = 0.839 nm.[9]

Magnetite differs from most other iron oxides in that it contains both divalent and trivalent iron[9].

As a member of the spinel group, magnetite can form "solid solutions with similarly structured minerals, including "ulvospinel (Fe2TiO4), "hercynite (FeAl2O4) and "chromite (FeCr2O4). Titanomagnetite, also known as titaniferous magnetite, is a solid solution between magnetite and ulvospinel that crystallizes in many "mafic igneous rocks. Titanomagnetite may undergo oxyexsolution during cooling, resulting in ingrowths of magnetite and ilmenite.

Crystal morphology and size[edit]

Natural and synthetic magnetite occurs most commonly as "octahedral crystals bounded by {111} planes and as "rhombic-dodecahedra[9]. Twinning occurs on the {111} plane.

Hydrothermal synthesis usually produce single octahedral crystals which can be as large as 10mm across[9]. In the presence of mineralizers such as 0.1M HI or 2M "NH4Cl and at 0.207 "MPa at 416-800°C, magnetite grew as crytals whose shapes were a combination of rhombic-dodechahedra forms[9]. 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[9].

Reactions[edit]

Magnetite has been important in understanding the conditions under which rocks form. Magnetite reacts with oxygen to produce "hematite, and the mineral pair forms a "buffer that can control oxygen "fugacity. Commonly, "igneous rocks contain solid solutions of both titanomagnetite and hemoilmenite or titanohematite. Compositions of the mineral pairs are used to calculate how oxidizing was the "magma (i.e., the "oxygen fugacity of the magma): a range of "oxidizing conditions are found in magmas and the oxidation state helps to determine how the magmas might evolve by "fractional crystallization. Magnetite also is produced from "peridotites and "dunites by "serpentinization.

Magnetic properties[edit]

Lodestones were used as an early form of "magnetic compass. Magnetite typically carries the dominant magnetic signature in rocks, and so it has been a critical tool in "paleomagnetism, a science important in understanding "plate tectonics and as historic data for "magnetohydrodynamics and other "scientific fields.

The relationships between magnetite and other iron-rich 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.

At low temperatures, magnetite undergoes a crystal structure phase transition from a monoclinic structure to a cubic structure known as the "Verwey transition. The Verwey transition occurs around 121 K and is dependent on grain size, domain state, and the iron-oxygen "stoichiometry.[10] An isotropic point also occurs near the Verwey transition around 130 K, at which point the sign of the magnetocrystalline anisotropy constant changes from positive to negative.[11] The "Curie temperature of magnetite is 858 K (585 °C; 1,085 °F).

Distribution of deposits[edit]

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Magnetite and other heavy minerals (dark) in a quartz "beach "sand ("Chennai, "India).

Magnetite is sometimes found in large quantities in beach sand. Such "black sands (mineral sands or iron sands) are found in various places, such as "Lung Kwu Tan of "Hong Kong; "California, "United States; and the west coast of the North Island of "New Zealand.[12] 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. These sedimentary rocks have been used to infer changes in the oxygen content of the atmosphere of the Earth.[13]

Large deposits of magnetite are also found in the "Atacama region of "Chile; the "Valentines region of "Uruguay; "Kiruna, "Sweden; the "Pilbara, Midwest and Northern Goldfields regions in "Western Australia; the "Eyre Peninsula in "South Australia; the "Tallawang Region of "New South Wales; and in the "Adirondack region of "New York in the "United States. "Kediet ej Jill, the highest mountain of "Mauritania, is made entirely of the mineral. Deposits are also found in "Norway, "Germany, "Italy, "Switzerland, "South Africa, "India, "Indonesia, "Mexico, "Hong Kong, and in "Oregon, "New Jersey, "Pennsylvania, "North Carolina, "West Virginia, "Virginia, "New Mexico, "Utah, and "Colorado in the "United States. 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.[14]

Magnetite crystals with a "cubic habit have been found in just one location: Balmat, "St. Lawrence County, New York.[15]

Biological occurrences[edit]

"Biomagnetism is usually related to the presence of biogenic crystals of magnetite, which occur widely in organisms.[16] These organisms range from "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.[17][18] Biomagnetites account for the effects of weak magnetic fields on biological systems.[19] There is also a chemical basis for cellular sensitivity to electric and magnetic fields ("galvanotaxis).[20]

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Magnetite magnetosomes in Gammaproteobacteria

Pure magnetite particles are "biomineralized in "magnetosomes, which are produced by several species of "magnetotactic 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.

Several species of birds are known to incorporate magnetite crystals in the upper beak for "magnetoreception,[21] which (in conjunction with "cryptochromes in the "retina) gives them the ability to sense the direction, "polarity, and magnitude of the ambient "magnetic field.[17][22]

"Chitons, a type of mollusk, have a tongue-like structure known as a "radula, covered with magnetite-coated teeth, or "denticles.[23] The hardness of the magnetite helps in breaking down food, and its magnetic properties may additionally aid in navigation. It has also been proposed that biological magnetite may store information.[24]

Human brain[edit]

There is also evidence that magnetite exists in the human brain,[18] where it is theorized to affect long-term memory.[25] Some researchers also suggest that humans possess a magnetic sense,[26] proposing that this could allow certain people to use magnetoreception for navigation.[27] 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.[28]

"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 "nanoparticles. 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. A further eight, aged 62 to 92, came from Manchester, and some had died with varying severities of neurodegenerative diseases.[29] According to researchers led by Prof. Barbara Maher at Lancaster University and published in the Proceedings of the National Academy of Sciences, such particles could conceivably contribute to diseases like "Alzheimer's disease. Though a causal link has not been established, laboratory studies suggest that iron oxides like magnetite are a component of "protein plaques in the brain, linked to Alzheimer's disease.[30]

Applications[edit]

Due to its high iron content, magnetite has long been a major "iron ore.[31] It is reduced in "blast furnaces to "pig iron or "sponge iron for conversion to "steel.

Magnetic recording[edit]

"Audio recording using magnetic acetate tape was developed in the 1930s. The German "magnetophon utilized magnetite powder as the recording medium.[32] Following "World War II, "3M Company continued work on the German design. In 1946, the 3M researchers found they could improve the magnetite-based tape, which utilized powders of cubic crystals, by replacing the magnetite with needle-shaped particles of "gamma ferric oxide (γ-Fe2O3).[32]

Catalysis[edit]

Magnetite is the catalyst for the industrial synthesis of "ammonia.[33]

Gallery of magnetite mineral specimens[edit]

See also[edit]

References[edit]

  1. ^ Handbook of Mineralogy
  2. ^ Mindat.org Mindat.org
  3. ^ Webmineral data
  4. ^ Hurlbut, Cornelius S.; Klein, Cornelis (1985). Manual of Mineralogy (20th ed.). Wiley. "ISBN "0-471-80580-7. 
  5. ^ a b c Hurlbut, Cornelius Searle; W. Edwin Sharp; Edward Salisbury Dana (1998). Dana's minerals and how to study them. John Wiley and Sons. p. 96. "ISBN "0-471-15677-9. 
  6. ^ Wasilewski, Peter; Günther Kletetschka (1999). "Lodestone: Nature's only permanent magnet - What it is and how it gets charged". "Geophysical Research Letters. 26 (15): 2275–78. "Bibcode:1999GeoRL..26.2275W. "doi:10.1029/1999GL900496. 
  7. ^ Harrison, R. J.; Dunin-Borkowski, RE; Putnis, A (2002). "Direct imaging of nanoscale magnetic interactions in minerals" (free-download pdf). Proceedings of the National Academy of Sciences. 99 (26): 16556–16561. "Bibcode:2002PNAS...9916556H. "doi:10.1073/pnas.262514499. "PMC 139182Freely accessible. "PMID 12482930. 
  8. ^ Maher, B. A.; Taylor, R. M. (1988). "Formation of ultrafine-grained magnetite in soils". Nature. 336: 368–370. "doi:10.1038/336368a0. 
  9. ^ a b c d e f Cornell; Schwertmann (1996). The Iron Oxides. New York: VCH. pp. 28–30. "ISBN "3-527-28576-8. 
  10. ^ "Influence of nonstoichiometry on the Verwey transition". Phys. Rev. B. 31: 430–436. 1985. "doi:10.1103/PhysRevB.31.430. 
  11. ^ Gubbins, D., & Herrero-Bervera, E. (Eds.). (2007). Encyclopedia of geomagnetism and paleomagnetism. Springer Science & Business Media.
  12. ^ Templeton, Fleur. "1. Iron – an abundant resource - Iron and steel". Te Ara Encyclopedia of New Zealand. Retrieved 4 January 2013. 
  13. ^ 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. "doi:10.2138/am.2005.1871. 
  14. ^ Ferrous Nonsnotus
  15. ^ "The mineral Magnetite information and pictures". Minerals.net. 
  16. ^ Kirschvink, J L; Walker, M M; Diebel, C E (2001). "Magnetite-based magnetoreception". Current Opinion in Neurobiology. 11 (4): 462–7. "doi:10.1016/s0959-4388(00)00235-x. "PMID 11502393. 
  17. ^ a b Wiltschko, Roswitha; Wiltschko, Wolfgang (2014). "Sensing magnetic directions in birds: radical pair processes involving cryptochrome". Biosensors. 4 (3): 221–42. "doi:10.3390/bios4030221. Lay summary. 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. 
  18. ^ a b Kirschvink, Joseph; (et al.) (1992). "Magnetite biomineralization in the human brain". Proceedings of the National Academy of Sciences of the USA. 89 (16): 7683–7687. "doi:10.1073/pnas.89.16.7683. Lay summaryUsing an ultrasensitive superconducting magnetometer in a clean-lab environment, we have detected the presence of ferromagnetic material in a variety of tissues from the human brain. 
  19. ^ 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. "PMID 1285705. Lay summary. 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. 
  20. ^ Nakajima, Ken-ichi; Zhu, Kan; Sun, Yao-Hui; Hegyi, Bence; Zeng, Qunli; Murphy, Christopher J; Small, J Victor; Chen-Izu, Ye; Izumiya, Yoshihiro; Penninger, Josef M; Zhao, Min (2015). "KCNJ15/Kir4.2 couples with polyamines to sense weak extracellular electric fields in galvanotaxis". Nature Communications. 6: 8532. "doi:10.1038/ncomms9532. "PMC 4603535Freely accessible. "PMID 26449415. Lay summary. Taken together these data suggest a previously unknown two-molecule sensing mechanism in which KCNJ15/Kir4.2 couples with polyamines in sensing weak electric fields. 
  21. ^ Kishkinev, D A; Chernetsov, N S (2014). "[Magnetoreception systems in birds: a review of current research]". Zhurnal obshcheĭ biologii. 75 (2): 104–23. Lay summary. There are good reasons to believe that this visual magnetoreceptor processes compass magnetic information which is necessary for migratory orientation. 
  22. ^ Wiltschko, Roswitha; Stapput, Katrin; Thalau, Peter; Wiltschko, Wolfgang (2010). "Directional orientation of birds by the magnetic field under different light conditions". Journal of the Royal Society, Interface / the Royal Society. 7 (Suppl 2): S163–77. "doi:10.1098/rsif.2009.0367.focus. "PMC 2843996Freely accessible. "PMID 19864263. Lay summaryCompass orientation controlled by the inclination compass ...allows birds to locate courses of different origin. 
  23. ^ Lowenstam, H A (1967). "Lepidocrocite, an apatite mineral, and magnetic in teeth of chitons (Polyplacophora)". Science. 156 (3780): 1373–1375. "doi:10.1126/science.156.3780.1373. "PMID 5610118. 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. 
  24. ^ Bókkon, Istvan; Salari, Vahid (2010). "Information storing by biomagnetites". Journal of biological physics. 36 (1): 109–20. "doi:10.1007/s10867-009-9173-9. "PMC 2791810Freely accessible. "PMID 19728122. 
  25. ^ Banaclocha, Marcos Arturo Martínez; Bókkon, István; Banaclocha, Helios Martínez (2010). "Long-term memory in brain magnetite". Medical Hypotheses. 74 (2): 254–7. "doi:10.1016/j.mehy.2009.09.024. "PMID 19815351. 
  26. ^ "Human Magnetoreception". 
  27. ^ Baker, R R (1988). "Human magnetoreception for navigation". Progress in clinical and biological research. 257: 63–80. "PMID 3344279. 
  28. ^ Kirschvink, Joseph L; Winklhofer, Michael; Walker, Michael M (2010). "Biophysics of magnetic orientation: strengthening the interface between theory and experimental design". Journal of the Royal Society, Interface / the Royal Society. 7 Suppl 2: S179–91. "doi:10.1098/rsif.2009.0491.focus. "PMC 2843999Freely accessible. "PMID 20071390. 
  29. ^ BBC Environment:Pollution particles 'get into brain'
  30. ^ Wilson, Clare (5 September 2016). "Air pollution is sending tiny magnetic particles into your brain". "New Scientist. 231 (3090). Retrieved 6 September 2016. 
  31. ^ Franz Oeters et al"Iron" in Ullmann's Encyclopedia of Industrial Chemistry, 2006, Wiley-VCH, Weinheim. "doi: 10.1002/14356007. a14_461.pub2
  32. ^ a b Schoenherr, Steven (2002). "The History of Magnetic Recording". Audio Engineering Society. 
  33. ^ Max Appl "Ammonia, 2. Production Processes" in Ullmann's Encyclopedia of Industrial Chemistry 2011, Wiley-VCH. "doi:10.1002/14356007.o02_o11

Further reading[edit]

External links[edit]

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