Editing Iron (section)

==Origin and occurrence in nature==
===Cosmogenesis===
Iron's abundance in [[Terrestrial planet|rocky planets]] like Earth is due to its abundant production during the runaway fusion and explosion of type [[Type Ia supernova|Ia supernovae]], which scatters the iron into space.<ref>{{Cite web |last=Aron |first=Jacob |title=Supernova space bullets could have seeded Earth's iron core |url=https://www.newscientist.com/article/dn27570-supernova-space-bullets-could-have-seeded-earths-iron-core/ |access-date=2020-10-02 |website=New Scientist |language=en-US}}</ref><ref>{{Cite web |last=Croswell |first=Ken |title=Iron in the Fire: The Little-Star Supernovae That Could |url=https://www.scientificamerican.com/article/little-star-supernovae-that-could-dwarf-stars/ |access-date=2021-01-03 |website=Scientific American |language=en}}</ref>

===Metallic iron===
[[File:Widmanstatten hand.jpg|thumb| right| A polished and chemically etched piece of an iron meteorite, believed to be similar in composition to the Earth's metallic core, showing individual crystals of the iron-nickel alloy ([[Widmanstatten pattern]])]]
Metallic or [[native iron]] is rarely found on the surface of the Earth because it tends to oxidize. However, both the Earth's [[inner core|inner]] and [[outer core]], which together account for 35% of the mass of the whole Earth, are believed to consist largely of an iron alloy, possibly with [[nickel]]. Electric currents in the liquid outer core are believed to be the origin of the [[Earth's magnetic field]]. The other [[terrestrial planet]]s ([[Mercury (planet)|Mercury]], [[Venus (planet)|Venus]], and [[Mars (planet)|Mars]]) as well as the [[Moon]] are believed to have a metallic core consisting mostly of iron. The [[M-type asteroid]]s are also believed to be partly or mostly made of metallic iron alloy.

The rare [[iron meteorite]]s are the main form of natural metallic iron on the Earth's surface. Items made of [[cold forging|cold-worked]] meteoritic iron have been found in various archaeological sites dating from a time when iron smelting had not yet been developed; and the [[Inuit people|Inuit]] in [[Greenland]] have been reported to use iron from the [[Cape York meteorite]] for tools and hunting weapons.<ref>{{cite journal|last=Buchwald |first= V F| title = On the Use of Iron by the Eskimos in Greenland| journal = Materials Characterization| volume = 29| issue = 2| year = 1992 | pages = 139–176 | doi = 10.1016/1044-5803(92)90112-U }}</ref> About 1 in 20 [[meteorite]]s consist of the unique iron-nickel minerals [[taenite]] (35–80% iron) and [[kamacite]] (90–95% iron).<ref>{{Cite book |url={{Google books|QDU7AAAAIAAJ|page=PA152|keywords=|text=|plainurl=yes}} |page=152 |title=Planet earth: cosmology, geology, and the evolution of life and environment |publisher=Cambridge University Press|first=Cesare|last=Emiliani |date=1992 |isbn=978-0-521-40949-0 |bibcode=1992pecg.book.....E}}</ref> Native iron is also rarely found in basalts that have formed from magmas that have come into contact with carbon-rich sedimentary rocks, which have reduced the oxygen [[fugacity]] sufficiently for iron to crystallize. This is known as [[telluric iron]] and is described from a few localities, such as [[Disko Island]] in West Greenland, [[Sakha Republic|Yakutia]] in [[Russia]] and [[Bühl (Baden)|Bühl]] in [[Germany]].<ref name="Pernet-Fisher_etal_2017">{{Cite journal |last1=Pernet-Fisher |first1=J. |last2=Day |first2=J.M.D. |last3=Howarth |first3=G.H. |last4=Ryabov |first4=V.V. |last5=Taylor |first5=L.A. |date=2017 |title=Atmospheric outgassing and native-iron formation during carbonaceous sediment–basalt melt interactions |url=https://www.researchgate.net/publication/312455203 |journal=Earth and Planetary Science Letters |volume=460 |pages=201–212 |doi=10.1016/j.epsl.2016.12.022|bibcode=2017E&PSL.460..201P |doi-access=free }}</ref>

===Mantle minerals===
[[Ferropericlase]] {{chem2|(Mg,Fe)O}}, a solid solution of [[periclase]] (MgO) and [[wüstite]] (FeO), makes up about 20% of the volume of the [[lower mantle]] of the Earth, which makes it the second most abundant mineral phase in that region after [[silicate perovskite]] {{chem2|(Mg,Fe)SiO3}}; it also is the major host for iron in the lower mantle.<ref>Stark, Anne M. (20 September 2007) [https://web.archive.org/web/20100527235247/https://publicaffairs.llnl.gov/news/news_releases/2007/NR-07-09-03.html Researchers locate mantle's spin transition zone, leading to clues about earth's structure]. [[Lawrence Livermore National Laboratory]]</ref> At the bottom of the [[Transition zone (Earth)|transition zone]] of the mantle, the reaction γ-{{chem2|(Mg,Fe)2[SiO4] ↔ (Mg,Fe)[SiO3] + (Mg,Fe)O}} transforms [[ringwoodite|γ-olivine]] into a mixture of silicate perovskite and ferropericlase and vice versa. In the literature, this mineral phase of the lower mantle is also often called magnesiowüstite.<ref name="Ferro">[https://www.mindat.org/min-35903.html Ferropericlase]. Mindat.org</ref> [[Silicate perovskite]] may form up to 93% of the lower mantle,<ref name="Murakami">{{cite journal |last=Murakami |first=M. |author2=Ohishi Y. |author3=Hirao N. |author4=Hirose K. |year=2012 |title=A perovskitic lower mantle inferred from high-pressure, high-temperature sound velocity data |journal=Nature |volume=485 |issue=7396 |pages=90–94|bibcode=2012Natur.485...90M |doi=10.1038/nature11004 |pmid=22552097 |s2cid=4387193}}</ref> and the magnesium iron form, {{chem2|(Mg,Fe)SiO3}}, is considered to be the most abundant [[mineral]] in the Earth, making up 38% of its volume.<ref name="Sharp">{{cite journal|last1=Sharp|first1=T.|title=Bridgmanite – named at last |journal=Science |date=27 November 2014 |volume=346 |issue=6213 |pages=1057–58 |doi=10.1126/science.1261887 |pmid=25430755 |bibcode=2014Sci...346.1057S |s2cid=206563252}}</ref>

===Earth's crust===
[[File:Roussillon_sentier_des_ocres2.JPG|thumb|Ochre path in [[Roussillon, Vaucluse|Roussillon]]]]

While iron is the most abundant element on Earth, most of this iron is concentrated in the [[Earth's inner core|inner]] and [[Earth's outer core|outer]] cores.<ref>{{Cite journal|last1=Kong|first1=L. T.|last2=Li|first2=J. F.|last3=Shi|first3=Q. W.|last4=Huang|first4=H. J.|last5=Zhao|first5=K.|date=2012-03-06|title=Dynamical stability of iron under high-temperature and high-pressure conditions|journal=EPL|volume=97|issue=5|pages=56004p1–56004p5|doi=10.1209/0295-5075/97/56004|bibcode=2012EL.....9756004K|s2cid=121861429 }}</ref><ref>{{Cite journal|last1=Gaminchev|first1=K. G.|last2=Chamati|first2=H.|date=2014-12-03|title=Dynamic stability of Fe under high pressure|journal=J. Phys.|volume=558|issue=1|pages=012013(1–7)|doi=10.1088/1742-6596/558/1/012013|bibcode=2014JPhCS.558a2013G|doi-access=free}}</ref> The fraction of iron that is in [[Crust (geology)|Earth's crust]] only amounts to about 5% of the overall mass of the crust and is thus only the fourth most abundant element in that layer (after [[oxygen]], [[silicon]], and [[aluminium]]).<ref>{{Cite journal|name-list-style=amp|date=1980|title=Chemical composition of Earth, Venus, and Mercury|journal=[[Proc. Natl. Acad. Sci.]]|volume=77|issue=12|pages=6973–77|bibcode=1980PNAS...77.6973M|doi=10.1073/pnas.77.12.6973|pmc=350422|pmid=16592930|last1=Morgan |first1= John W. |last2=Anders |first2= Edward |doi-access=free}}</ref>

Most of the iron in the crust is combined with various other elements to form many [[Iron ore|iron minerals]]. An important class is the [[iron oxide]] minerals such as [[hematite]] (Fe<sub>2</sub>O<sub>3</sub>), [[magnetite]] (Fe<sub>3</sub>O<sub>4</sub>), and [[siderite]] (FeCO<sub>3</sub>), which are the major [[iron ore|ores of iron]]. Many [[igneous rock]]s also contain the sulfide minerals [[pyrrhotite]] and [[pentlandite]].<ref name="mindat">{{cite web|url=https://www.mindat.org/min-3328.html |publisher=Mindat.org| title=Pyrrhotite|access-date=2009-07-07}}</ref><ref name="Klein">Klein, Cornelis and Cornelius S. Hurlbut, Jr. (1985) ''Manual of Mineralogy,'' Wiley, 20th ed, pp. 278–79 {{ISBN|0-471-80580-7}}</ref> During [[weathering]], iron tends to leach from sulfide deposits as the sulfate and from silicate deposits as the bicarbonate. Both of these are oxidized in aqueous solution and precipitate in even mildly elevated pH as [[iron(III) oxide]].{{sfn|Greenwood|Earnshaw|1997|p=1071}}

[[File:Outcropping banded iron formation - panoramio.jpg|thumb|Banded iron formation in McKinley Park, Minnesota]]
Large deposits of iron are [[banded iron formations]], a type of rock consisting of repeated thin layers of iron oxides alternating with bands of iron-poor [[shale]] and [[chert]]. The banded iron formations were laid down in the time between {{Ma|3700}} and {{Ma|1800}}.<ref>{{Cite journal| first1 = T. W.|last2 = Reinhard|title = Early Earth: Oxygen for heavy-metal fans|journal = Nature|volume = 461|issue = 7261|pages = 179–181|date = 2009|last1 = Lyons|doi = 10.1038/461179a|pmid = 19741692|first2 = C. T.|bibcode=2009Natur.461..179L|s2cid = 205049360|doi-access = free}}</ref><ref>{{Cite journal| first1 = P.|title = Paleoecological Significance of the Banded Iron-Formation|journal = Economic Geology|volume = 68|last1 = Cloud|pages = 1135–43|date = 1973|doi = 10.2113/gsecongeo.68.7.1135| issue = 7| bibcode=1973EcGeo..68.1135C }}</ref>

Materials containing finely ground iron(III) oxides or oxide-hydroxides, such as [[ochre]], have been used as yellow, red, and brown [[pigment]]s since pre-historical times. They contribute as well to the color of various rocks and [[clay]]s, including entire geological formations like the [[Painted Hills]] in [[Oregon]] and the [[Buntsandstein]] ("colored sandstone", British [[Bunter (geology)|Bunter]]).<ref>Dickinson, Robert E. (1964). ''Germany: A regional and economic geography'' (2nd ed.). London: Methuen.</ref> Through ''Eisensandstein'' (a [[Brown Jurassic|jurassic]] 'iron sandstone', e.g. from [[Donzdorf]] in Germany)<ref>[https://web.archive.org/web/20040913020231/https://www.lgrb.uni-freiburg.de/lgrb/Fachbereiche/rohstoffgeologie/grundlagen/lagerstaetten/naturwerksteine ''Naturwerksteine in Baden-Württemberg.''] Landesamt für Geologie, Rohstoffe und Bergbau, Baden-Württemberg</ref> and [[Bath stone]] in the UK, iron compounds are responsible for the yellowish color of many historical buildings and sculptures.<ref>{{cite web|url=https://minervaconservation.com/articles/talesfromtheriverbank.html|title=Tales From The Riverbank|publisher=Minerva Stone Conservation|access-date=22 September 2015|archive-date=28 September 2015|archive-url=https://web.archive.org/web/20150928031602/http://www.minervaconservation.com/articles/talesfromtheriverbank.html|url-status=dead}}</ref> The proverbial [[Mars surface color|red color of the surface of Mars]] is derived from an iron oxide-rich [[regolith]].<ref>{{Cite journal|last2=Morris|first2=R. V.|last3=Souza|first3=P. A.|last4=Rodionov|first4=D.|last5=Schröder|first5=C.|date=2007|title=Two earth years of Mössbauer studies of the surface of Mars with MIMOS II|journal=Hyperfine Interactions|volume=170|issue=1–3|pages=169–77|bibcode=2006HyInt.170..169K|doi=10.1007/s10751-007-9508-5|last1=Klingelhöfer|first1=G.|s2cid=98227499}}</ref>

Significant amounts of iron occur in the iron sulfide mineral [[pyrite]] (FeS<sub>2</sub>), but it is difficult to extract iron from it and it is therefore not exploited.<ref>{{cite book | last1=Winderlich | first1=R. | last2=Peter | first2=W. | title=Lehrbuch der Chemie für Höhere Lehranstalten : Einheitsausgabe für Unter- und Oberstufe | publication-place=Wiesbaden | date=1954 | isbn=978-3-663-04370-6 | oclc=913701506 | language=de|page=75 |publisher=Vieweg+Teubner Verlag }}</ref> In fact, iron is so common that production generally focuses only on ores with very high quantities of it.<ref>{{cite book | last=Bertau | first=Martin | title=Industrielle Anorganische Chemie | publisher=Wiley-VCH | publication-place=Weinheim | date=2013 | isbn=978-3-527-64956-3 | oclc=855858511 | language=de|page=696}}</ref>

According to the [[International Resource Panel]]'s [[Metal Stocks in Society report]], the global stock of iron in use in society is 2,200 kg per capita. More-developed countries differ in this respect from less-developed countries (7,000–14,000 vs 2,000 kg per capita).<ref>[https://archive.today/20120914112201/https://www.unep.org/resourcepanel/Publications/MetalStocks/tabid/56054/Default.aspx ''Metal Stocks in Society: Scientific synthesis''], 2010, [[International Resource Panel]], [[UNEP]]</ref>

===Oceans===
Ocean science demonstrated the role of the iron in the ancient seas in both marine biota and climate.<ref>{{cite journal | last=Stoll | first=Heather | title=30 years of the iron hypothesis of ice ages | journal=Nature | publisher=Springer Science and Business Media LLC | volume=578 | issue=7795 | date=2020-02-17 | issn=0028-0836 | doi=10.1038/d41586-020-00393-x | pages=370–371| pmid=32066927 | bibcode=2020Natur.578..370S | s2cid=211139074 }}</ref>