Magnetite

Magnetite

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 is 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.

Properties

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]

Solid solutions

Magnetite has an inverse spinel crystal structure. As a member of the spinel group, it 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.

Reactions

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

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.[9] 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. [10] The Curie temperature of magnetite is 858 K (585 °C; 1,085 °F).

Distribution of deposits

A fine textured sample, ~5cm across
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 California and the west coast of the North Island of New Zealand.[11] The magnetite is carried to the beach via rivers from erosion and is concentrated via 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.

Large deposits of magnetite are also found in the Atacama region of Chile, Valentines region of Uruguay, Kiruna, Sweden, the Pilbara, Midwest and Northern Goldfields regions in Western Australia, New South Wales in the Tallawang Region, 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.[12] Deposits are also found in Norway, Germany, Italy, Switzerland, South Africa, India, Indonesia, Mexico, 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.[13]

Biological occurrences

Biomagnetism is usually related to the presence of biogenic crystals of magnetite, which occur widely in organisms.[14] 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.[15][16] Biomagnetites account for the effects of weak magnetic fields on biological systems.[17] There is also a chemical basis for cellular sensitivity to electric and magnetic fields (galvanotaxis).[18]

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,[19] which (in conjunction with cryptochromes in the retina) gives them the ability to sense the direction, polarity, and magnitude of the ambient magnetic field.[15][20]

Chitons, a type of mollusk, have a tongue-like structure known as a radula, covered with magnetite-coated teeth, or denticles.[21] 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.[22]

Human brain

There is also evidence that magnetite exists in the human brain.[16] It is proposed that this could allow certain individuals to use magnetoreception for navigation.[23] More generally, magnetite in the brain is theorized to affect long-term memory,[24] and some researchers suggest that humans possess a magnetic sense.[25] It has not been understood up to now due to a lag in applying more modern research techniques to the study of magnetic phenomena in biological contexts.[26]

Magnetite particles were found in the brains from 37 people - 29 who had lived and died in Mexico City, a significant air pollution hotspot, and who were aged from 3 to 85. A further eight came from Manchester, were aged 62-92 and some had died with varying severities of neurodegenerative diseases. [27]

Although magnetite can occur naturally in the brain in biologically formed jagged particles, those supposedly from air pollution are said to have a spherical form. 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 evidence for this is lacking.

Electron microscope scans of human brain-tissue samples have differentiated between crystalline forms of magnetite in the brain, which are naturally produced in body cells, and rounded nanoparticles incorporated from environmental pollution; the pollution-related magnetite particles outnumber the particles of natural origin by one hundred to one. Laboratory studies suggest that iron oxide is a component of protein plaques in the brain, linked to Alzheimer's disease.[28]

Applications

Due to its high iron content, magnetite has long been a major iron ore.[29] It is reduced in blast furnaces to pig iron or sponge iron for conversion to steel.

Magnetic recording

Audio recording using magnetic acetate tape was developed in the 1930s. The German magnetophon utilized magnetite powder as the recording medium.[30] Following World War II, the 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).[30]

Catalysis

Magnetite is the catalyst for the industrial synthesis of ammonia.[31]

Gallery of magnetite mineral specimens

See also

References

  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. 1 2 3 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.
  9. ↑ Influence of nonstoichiometry on the Verwey transition" Phys. Rev. 1985, B 31, 430. http://dx.doi.org/10.1103/PhysRevB.31.430
  10. ↑ Gubbins, D., & Herrero-Bervera, E. (Eds.). (2007). Encyclopedia of geomagnetism and paleomagnetism. Springer Science & Business Media.
  11. ↑ Templeton, Fleur. "1. Iron – an abundant resource - Iron and steel". Te Ara Encyclopedia of New Zealand. Retrieved 4 January 2013.
  12. ↑ Kediet ej Jill
  13. ↑ Ferrous Nonsnotus
  14. ↑ 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.
  15. 1 2 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.
  16. 1 2 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 summary – Using 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.
  17. ↑ 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.
  18. ↑ 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.
  19. ↑ 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.
  20. ↑ 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. PMID 19864263. Lay summary – Compass orientation controlled by the inclination compass ...allows birds to locate courses of different origin.
  21. ↑ 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.
  22. ↑ Bókkon, Istvan; Salari, Vahid (2010). "Information storing by biomagnetites.". Journal of biological physics. 36 (1): 109–20. doi:10.1007/s10867-009-9173-9. PMID 19728122.
  23. ↑ Baker, R R (1988). "Human magnetoreception for navigation". Progress in clinical and biological research. 257: 63–80. PMID 3344279.
  24. ↑ 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.
  25. ↑ "Human Magnetoreception".
  26. ↑ 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.
  27. ↑ BBC Environment:Pollution particles 'get into brain'
  28. ↑ Wilson, Clare (5 September 2016). "Air pollution is sending tiny magnetic particles into your brain". New Scientist. 231 (3090). Retrieved 6 September 2016.
  29. ↑ Franz Oeters et al"Iron" in Ullmann's Encyclopedia of Industrial Chemistry, 2006, Wiley-VCH, Weinheim. doi: 10.1002/14356007. a14_461.pub2
  30. 1 2 Schoenherr, Steven, 2002, The History of Magnetic Recording, Audio Engineering Society
  31. ↑ Max Appl "Ammonia, 2. Production Processes" in Ullmann's Encyclopedia of Industrial Chemistry 2011, Wiley-VCH. doi:10.1002/14356007.o02_o11

Further reading

External links

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