Editing Rare-earth element (section)

==Geological distribution==
[[File:Elemental abundances.svg|thumb|upright=2|The abundance of elements in Earth's crust per million Si atoms (''y'' axis is logarithmic)]]
As seen in the chart, rare-earth elements are found on Earth at similar concentrations to many common transition metals. The most abundant rare-earth element is [[cerium]], which is actually the 25th most abundant element in [[crust (geology)|Earth's crust]], having 68 parts per million (about as common as copper). The exception is the highly unstable and radioactive [[promethium]] "rare earth" is quite scarce. The longest-lived isotope of promethium has a half-life of 17.7 years, so the element exists in nature in only negligible amounts (approximately 572&nbsp;g in the entire Earth's crust).<ref>{{cite journal |author1=P. Belli |author2=R. Bernabei |author3=F. Cappella |author4=R. Cerulli |author5=C. J. Dai |author6=F. A. Danevich |author7=A. d'Angelo |author8=A. Incicchitti |author9=V. V. Kobychev |author10=S. S. Nagorny |author11=S. Nisi |author12=F. Nozzoli |author13=D. Prosperi |author14=V. I. Tretyak |author15=S. S. Yurchenko |year=2007 |title=Search for α decay of natural Europium |journal=Nuclear Physics A |volume=789 |issue=1–4 |pages=15–29 |doi=10.1016/j.nuclphysa.2007.03.001 |bibcode=2007NuPhA.789...15B}}</ref> Promethium is one of the two elements that do not have stable (non-radioactive) isotopes and are followed by (i.e. with higher atomic number) stable elements (the other being [[technetium]]).

The rare-earth elements are often found together. During the sequential [[accretion (geology)|accretion]] of the Earth, the dense rare-earth elements were incorporated into the deeper portions of the planet. Early differentiation of molten material largely incorporated the rare earths into [[Mantle (geology)|mantle]] rocks.<ref name="winter">{{cite book |title=Principles of igneous and metamorphic petrology |last=Winter |first=John D. |date=2010 |publisher=Prentice Hall |isbn=978-0-321-59257-6 |edition=2nd |location=New York |oclc=262694332}}</ref> The [[magnetic moment|high field strength]]{{Clarify|date=April 2021}} and large [[ionic radius|ionic radii]] of rare earths make them incompatible with the crystal lattices of most rock-forming minerals, so REE will undergo strong partitioning into a melt phase if one is present.<ref name="winter"/> 

REE are chemically very similar and have always been difficult to separate, but the gradual decrease in ionic radius from light REE (LREE) to heavy REE (HREE), called the [[lanthanide contraction]], can produce a broad separation between light and heavy REE. The larger ionic radii of LREE make them generally more incompatible than HREE in rock-forming minerals, and will partition more strongly into a melt phase, while HREE may prefer to remain in the crystalline residue, particularly if it contains HREE-compatible minerals like [[garnet]].<ref name="winter"/><ref name="Michel">{{cite book |title=Geology of mineral resources |last1=Jébrak |first1=Michel |last2=Marcoux |first2=Eric |last3=Laithier |first3=Michelle |last4=Skipwith |first4=Patrick |publisher=Geological Association of Canada |isbn=978-1-897095-73-7 |edition=2nd |location=St. John's, NL |oclc=933724718 |year=2014}}</ref> The result is that all magma formed from partial melting will always have greater concentrations of LREE than HREE, and individual minerals may be dominated by either HREE or LREE, depending on which range of ionic radii best fits the crystal lattice.<ref name="winter"/>

Among the anhydrous rare-earth phosphates, it is the tetragonal mineral [[xenotime]] that incorporates yttrium and the HREE, whereas the monoclinic [[monazite]] phase incorporates cerium and the LREE preferentially. The smaller size of the HREE allows greater solid solubility in the rock-forming minerals that make up Earth's mantle, and thus yttrium and the HREE show less enrichment in Earth's crust relative to [[chondrite|chondritic]] abundance than does cerium and the LREE.<ref name=Powell/>

This has economic consequences: large ore bodies of LREE are known around the world and are being exploited. Ore bodies for HREE are more rare, smaller, and less concentrated. Most of the current supply of HREE originates in the "ion-absorption clay" ores of Southern China. Some versions provide concentrates containing about 65% yttrium oxide, with the HREE being present in ratios reflecting the [[Oddo–Harkins rule]]: even-numbered REE at abundances of about 5% each, and odd-numbered REE at abundances of about 1% each. Similar compositions are found in xenotime or gadolinite.<ref name=Powell/>

Well-known minerals containing yttrium, and other HREE, include gadolinite, xenotime, [[samarskite]], [[euxenite]], [[fergusonite]], yttrotantalite, yttrotungstite, yttrofluorite (a variety of [[fluorite]]), thalenite, and [[yttrialite]]. Small amounts occur in [[zircon]], which derives its typical yellow fluorescence from some of the accompanying HREE. The [[zirconium]] mineral [[eudialyte]], such as is found in southern [[Greenland]], contains small but potentially useful amounts of yttrium. Of the above yttrium minerals, most played a part in providing research quantities of lanthanides during the discovery days. [[Xenotime]] is occasionally recovered as a byproduct of heavy-sand processing, but is not as abundant as the similarly recovered [[monazite]] (which typically contains a few percent of yttrium). Uranium ores from Ontario have occasionally yielded yttrium as a byproduct.<ref name=Powell/>

Well-known minerals containing cerium, and other LREE, include [[bastnäsite]], [[monazite]], [[allanite]], [[loparite]], [[ancylite]], [[parisite]], [[lanthanite]], chevkinite, [[cerite]], [[stillwellite]], britholite, [[fluocerite]], and cerianite. Monazite (marine sands from [[Brazil]], [[India]], or [[Australia]]; rock from [[South Africa]]), bastnäsite (from [[Mountain Pass rare earth mine]], or several localities in China), and [[loparite]] ([[Kola Peninsula]], [[Russia]]) have been the principal ores of cerium and the light lanthanides.<ref name=Powell/>

Enriched deposits of rare-earth elements at the surface of the Earth, [[carbonatite]]s and [[pegmatite]]s, are related to alkaline [[plutonism]], an uncommon kind of magmatism that occurs in tectonic settings where there is rifting or that are near [[subduction]] zones.<ref name=Michel/> In a rift setting, the alkaline magma is produced by very small degrees of partial melting (<1%) of garnet peridotite in the [[upper mantle (Earth)|upper mantle]] (200 to 600&nbsp;km depth).<ref name=Michel/> This melt becomes enriched in incompatible elements, like the rare-earth elements, by leaching them out of the crystalline residue. The resultant magma rises as a [[diapir]], or [[diatreme]], along pre-existing fractures, and can be emplaced deep in [[crust (geology)|the crust]], or erupted at the surface.<ref name=winter/><ref name=Michel/>

Typical REE enriched deposits types forming in rift settings are carbonatites, and A- and M-Type granitoids.<ref name=winter/><ref name=Michel/> Near subduction zones, partial melting of the subducting plate within the [[asthenosphere]] (80 to 200&nbsp;km depth) produces a volatile-rich magma (high concentrations of {{CO2}} and water), with high concentrations of alkaline elements, and high element mobility that the rare earths are strongly partitioned into.<ref name=winter/> This melt may also rise along pre-existing fractures, and be emplaced in the crust above the subducting slab or erupted at the surface. REE-enriched deposits forming from these melts are typically S-Type granitoids.<ref name=winter/><ref name=Michel/>

Alkaline magmas enriched with rare-earth elements include carbonatites, peralkaline granites (pegmatites), and [[nepheline syenite]]. [[Carbonatite]]s crystallize from {{CO2}}-rich fluids, which can be produced by partial melting of hydrous-carbonated [[lherzolite]] to produce a CO{{sub|2}}-rich primary magma, by [[fractional crystallization (geology)|fractional crystallization]] of an alkaline primary magma, or by separation of a {{CO2}}-rich immiscible liquid from.<ref name=winter/><ref name=Michel/> These liquids are most commonly forming in association with very deep Precambrian [[craton]]s, like the ones found in Africa and the Canadian Shield.<ref name=winter/> 

Ferrocarbonatites are the most common type of carbonatite to be enriched in REE, and are often emplaced as late-stage, [[breccia]]ted pipes at the core of igneous complexes. They consist of fine-grained calcite and hematite, sometimes with significant concentrations of ankerite and minor concentrations of siderite.<ref name=winter/><ref name=Michel/> Large carbonatite deposits enriched in rare-earth elements include Mount Weld in Australia, Thor Lake in Canada, Zandkopsdrift in South Africa, and [[Mountain Pass rare earth mine|Mountain Pass]] in the USA.<ref name=Michel/> 

[[Pegmatite|Peralkaline granites]] (A-Type granitoids) have very high concentrations of alkaline elements and very low concentrations of phosphorus; they are deposited at moderate depths in extensional zones, often as igneous ring complexes, or as pipes, massive bodies, and lenses.<ref name=winter/><ref name=Michel/> These fluids have very low viscosities and high element mobility, which allows for the crystallization of large grains, despite a relatively short crystallization time upon emplacement; their large grain size is why these deposits are commonly referred to as pegmatites.<ref name=Michel/> 

Economically viable pegmatites include Niobium-Yttrium-Fluorine (NYF) types enriched in Yttrium and other rare-earth minerals, with REE-rich deposits found at Strange Lake in Canada and Khaladean-Buregtey in Mongolia.<ref name=Michel/> Nepheline syenite (M-Type granitoids) deposits are 90% feldspar and feldspathoid minerals. They are deposited in small, circular massifs and contain high concentrations of [[rare-earth mineral|rare-earth-bearing accessory minerals]].<ref name=winter/><ref name=Michel/> For the most part, these deposits are small but important examples include Illimaussaq-Kvanefeld in Greenland, and Lovozera in Russia.<ref name=Michel/>

Rare-earth elements can also be enriched in deposits by secondary alteration either by interactions with hydrothermal fluids or meteoric water or by erosion and transport of resistate REE-bearing minerals. [[Argillization]] of primary minerals enriches insoluble elements by leaching out silica and other soluble elements, recrystallizing feldspar into clay minerals such kaolinite, halloysite, and montmorillonite. In tropical regions where precipitation is high, weathering forms a thick argillized regolith, this process is called supergene enrichment and produces [[laterite]] deposits. Heavy rare-earth elements are incorporated into the residual clay by absorption. This kind of deposit is only mined for REE in Southern China, where the majority of global heavy rare-earth element production occurs. REE-laterites do form elsewhere, including over the carbonatite at Mount Weld in Australia. REE may also be extracted from placer deposits if the sedimentary parent lithology contains REE-bearing, heavy resistate minerals.<ref name=Michel/>

In 2011, Yasuhiro Kato, a geologist at the [[University of Tokyo]] who led a study of Pacific Ocean seabed mud, published results indicating the mud could hold rich concentrations of rare-earth minerals. The deposits, studied at 78 sites, came from "[h]ot plumes from hydrothermal vents pull[ing] these materials out of seawater and deposit[ing] them on the seafloor, bit by bit, over tens of millions of years. One square patch of metal-rich mud 2.3 kilometers wide might contain enough rare earths to meet most of the global demand for a year, Japanese geologists report in ''[[Nature Geoscience]]''." "I believe that rare[-]earth resources undersea are much more promising than on-land resources," said Kato. "[C]oncentrations of rare earths were comparable to those found in clays mined in China. Some deposits contained twice as much heavy rare earths such as dysprosium, a component of magnets in hybrid car motors."<ref name=Powell>Powell, Devin, [https://www.sciencenews.org/article/rare-earth-elements-plentiful-ocean-sediments "Rare earth elements plentiful in ocean sediments"], ''[[ScienceNews]]'', 3 July 2011. Via Kurt Brouwer's [http://blogs.marketwatch.com/fundmastery/2011/07/05/rare-earth-supply-demand/ Fundmastery Blog] {{Webarchive|url=https://web.archive.org/web/20110710022849/http://blogs.marketwatch.com/fundmastery/2011/07/05/rare-earth-supply-demand/ |date=July 10, 2011}}, ''MarketWatch'', 2011-07-05. Retrieved 2011-07-05.</ref><ref>{{cite journal |last1=Kato |first1=Yasuhiro |last2=Fujinaga |first2=Koichiro |last3=Nakamura |first3=Kentaro |last4=Takaya |first4=Yutaro |last5=Kitamura |first5=Kenichi |last6=Ohta |first6=Junichiro |last7=Toda |first7=Ryuichi |last8=Nakashima |first8=Takuya |last9=Iwamori |first9=Hikaru |date=2011 |title=Deep-sea mud in the Pacific Ocean as a potential resource for rare-earth elements |url=https://www.nature.com/articles/ngeo1185 |journal=Nature Geoscience |language=en |volume=4 |issue=8 |pages=535–539 |doi=10.1038/ngeo1185 |bibcode=2011NatGe...4..535K |issn=1752-0908|url-access=subscription }}</ref>

The global demand for rare-earth elements (REEs) is expected to increase more than fivefold by 2030.<ref>{{Cite web |title=Press corner |url=https://ec.europa.eu/commission/presscorner/home/en |access-date=2023-11-30 |website=European Commission - European Commission |language=en}}</ref><ref name=":170">{{Cite news |title=Europe Must Get Serious About Critical Minerals |url=https://www.eib.org/en/stories/critical-raw-materials-europe |access-date=2023-09-25 |website=European Investment Bank |language=en}}</ref>