Magnetite
Magnetite | |
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Magnetite and pyrite from Piedmont, Italy | |
General | |
Category |
Oxide minerals Spinel group Spinel structural group |
Formula (repeating unit) | iron(II,III) oxide, Fe2+Fe3+2O4 |
Strunz classification | 04.BB.05 |
Crystal symmetry | Isometric 4/m 3 2/m |
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 |
Crystal system | Isometric Hexoctahedral |
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, one of the three common naturally occurring iron oxides (chemical formula Fe3O4) and a member of the spinel group. Magnetite is the most magnetic of all the naturally occurring minerals on Earth.[5] Naturally magnetized pieces of magnetite, called lodestone, will attract small pieces of iron, and this was how ancient people first noticed the property of magnetism.
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 a black streak.
The chemical IUPAC name is iron(II,III) oxide and the common chemical name is ferrous-ferric oxide.
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.
Magnetite has been very 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 grains of two solid solutions, one of magnetite and ulvospinel and the other of ilmenite and hematite. 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 occurs in many sedimentary rocks, including banded iron formations. In many igneous rocks, magnetite-rich and ilmenite-rich grains occur that precipitated together in magma. Magnetite also is produced from peridotites and dunites by serpentinization.
The Curie temperature of magnetite is 858 K (585 °C; 1,085 °F).
Distribution of deposits
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.[6] 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.[7] Deposits are also found in Norway, Germany, Italy, Switzerland, South Africa, India, Indonesia, Mexico, and in Oregon, New Jersey, Pennsylvania, North Carolina, 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.[8]
Biological occurrences
Biomagnetism is usually related to the presence of biogenic[9] crystals of magnetite, which occur widely in organisms.[10] These organisms range from bacteria (e.g., Magnetospirillum magnetotacticum) to animals, where these crystals are found in the brain.[11] These crystals are involved in magnetoreception, the ability to sense the polarity or the inclination of the Earth's magnetic field, and aid in navigation. [9]
Chitons have teeth made of magnetite on their radula.[9]
Applications
Magnetic recording
Audio recording using magnetic acetate tape was developed in the 1930s. The German magnetophon utilized magnetite powder as the recording medium.[12] Following World War 2 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).[12]
Catalysis
Magnetite is the catalyst for the industrial synthesis of ammonia.[13]
Arsenic sorbent
Magnetite powder efficiently removes arsenic(III) and arsenic(V) from water, the efficiency of which increases ~200 times when the magnetite particle size decreases from 300 to 12 nm.[14] Arsenic-contaminated drinking water is a major problem around the world, which can be solved using magnetite as a sorbent.
Other
Because of its stability at high temperatures, it is used for coating industrial watertube steam boilers. The magnetite layer is formed after a chemical treatment (e.g. by using hydrazine).
Iron-metabolizing bacteria can trigger redox reactions in microscopic magnetite particles. Using light, magnetite can reduce chromium (VI) (its toxic form), converting it to less toxic chromium (III), which can then be incorporated into a harmless magnetite crystal. Phototrophic Rhodopseudomonas palustris oxidized the magnetite, while Geobacter sulfurreducens reduced it, readying it for another cycle.[15]
Gallery of magnetite mineral specimens
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Octahedral crystals of magnetite up to 1.8 cm across, on cream colored Feldspar crystals. Locality: Cerro Huañaquino, Potosí Department, Bolivia. Size: 8.4 x 5.2 x 3.2 cm.
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Unusual octahedral magnetite & chalcopyrite association, Aggeneys, Northern Cape Province, South Africa. Size 7 x 6 x 4 cm.
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Red gem-like crystals of Chondrodite with magnetite, Tilly Foster mine, Brewster, New York USA. Size 2.8 x 2.6 x 2.1 cm.
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Unusual specular hematite pseudomorph after magnetite, from Payun Matru volcano, Reserva Provincial La Payunia, Argentina. Size: 11.8 x 5.6 x 4.4 cm.
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Metallic, jet black, complex cubes of magnetite, from ZCA Mine No. 4, Balmat-Edwards district, St. Lawrence County, New York USA. Field of view, about 4 cm.
See also
- Bluing (steel), a process in which steel is partially protected against rust by a layer of magnetite
- Buena Vista Iron Ore District
- Corrosion product
- Ferrite
- Greigite
- Maghemite
- Magnesia (in natural mixtures with magnetite)
- Magnetotactic bacteria
- Mill scale
- Mineral redox buffer
- Magnes the shepherd
References
- ↑ Handbook of Mineralogy
- ↑ Mindat.org Mindat.org
- ↑ Webmineral data
- ↑ Hurlbut, Cornelius S.; Klein, Cornelis (1985). Manual of Mineralogy (20th ed.). Wiley. ISBN 0-471-80580-7.
- ↑ 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 139182. PMID 12482930.
- ↑ Templeton, Fleur (15 Jun 3 2010). "1. Iron – an abundant resource - Iron and steel". Te Ara Encyclopedia of New Zealand. Retrieved 4 January 2013. Check date values in:
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(help) - ↑ Kediet ej Jill
- ↑ Ferrous Nonsnotus
- ↑ 9.0 9.1 9.2 Magnetite in Human Tissues: A Mechanism for the Biological Effects of Weak ELF Magnetic Fields Joseph L. Kirschvink, Atsuko Kobayashi-Kirschvink, Juan C. Diaz- Ricci, and Steven J. Kirschvink
- ↑ Lowenstam, H. A. (1981). "Minerals formed by organisms". Science 211: 1126–31. doi:10.1126/science.7008198. PMID 7008198.
- ↑ Baker, R R; J G Mather; J H Kennaugh (1983-01-06). "Magnetic bones in human sinuses". Nature 301 (5895): 79–80. Bibcode:1983Natur.301...78R. doi:10.1038/301078a0. PMID 6823284.
- ↑ 12.0 12.1 Schoenherr, Steven, 2002, The History of Magnetic Recording, Audio Engineering Society
- ↑ Max Appl "Ammonia, 2. Production Processes" in Ullmann's Encyclopedia of Industrial Chemistry 2011, Wiley-VCH. doi:10.1002/14356007.o02_o11
- ↑ J.T. Mayo et al. (2007). "The effect of nanocrystalline magnetite size on arsenic removal". Sci. Technol. Adv. Mater. (FREE DOWNLOAD) 8: 71–75. Bibcode:2007STAdM...8...71M. doi:10.1016/j.stam.2006.10.005.
- ↑ "How bacteria can use magnetic particles to create a ‘natural battery’". KurzweilAI. March 30, 2015. Retrieved April 2015.
Further reading
- Lowenstam, Heinz A.; Weiner, Stephen (1989). On Biomineralization. USA: Oxford University Press. ISBN 0-19-504977-2.
- Chang, Shih-Bin Robin; Kirschvink, Joseph Lynn (1989). "Magnetofossils, the Magnetization of Sediments, and the Evolution of Magnetite Biomineralization" (PDF). Annual Review of Earth and Planetary Sciences 17: 169–195. Bibcode:1989AREPS..17..169C. doi:10.1146/annurev.ea.17.050189.001125.
External links
- Mineral galleries
- Bio-magnetics
- History of Magnetite Mining in the NJ Highlands
- Magnetite mining in New Zealand Accessed 25-Mar-09
- Mineral Survey of Santa Cruz County - Black Sand
- Peruvian sand dunes
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