Editing Samarium (section)

==Occurrence and production==
[[File:Samarskite-fresh.jpg|thumb|Samarskite|alt=Samarskite]]
Samarium concentration in soils varies between 2 and 23&nbsp;ppm, and oceans contain about 0.5–0.8&nbsp;parts per trillion.<ref name="emsley" /> The median value for its [[Abundance of elements in Earth's crust|abundance in the Earth's crust]] used by the CRC Handbook is 7 parts per million (ppm)<ref name=CRCabundance>ABUNDANCE OF ELEMENTS IN THE EARTH’S CRUST AND IN THE SEA, ''CRC Handbook of Chemistry and Physics,'' 97th edition (2016–2017), p. 14-17</ref> and is the 40th most abundant element.<ref>{{Cite book |last=Emsley |first=John |url=https://books.google.com/books?id=2EfYXzwPo3UC&dq=%2240th+most+abundant+element%22&pg=PA466 |title=Nature's Building Blocks: An A-Z Guide to the Elements |date=2011-08-25 |publisher=OUP Oxford |isbn=978-0-19-960563-7 |language=en}}</ref> Distribution of samarium in soils strongly depends on its chemical state and is very inhomogeneous: in sandy soils, samarium concentration is about 200 times higher at the surface of soil particles than in the water trapped between them, and this ratio can exceed 1,000 in clays.<ref name="LA2" />

Samarium is not found free in nature, but, like other rare earth elements, is contained in many minerals, including [[monazite]], [[bastnäsite]], [[cerite]], [[gadolinite]] and [[samarskite]]; monazite (in which samarium occurs at concentrations of up to 2.8%)<ref name="CRC" /> and bastnäsite are mostly used as commercial sources. World resources of samarium are estimated at two million [[tonne]]s; they are mostly located in China, US, Brazil, India, Sri Lanka and Australia, and the annual production is about 700 tonnes.<ref name="emsley" /> Country production reports are usually given for all rare-earth metals combined. By far, China has the largest production with 120,000 tonnes mined per year; it is followed by the US (about 5,000&nbsp;tonnes)<ref name="LA2" /> and India (2,700&nbsp;tonnes).<ref>{{cite web|url=http://minerals.usgs.gov/minerals/pubs/commodity/rare_earths/mcs-2010-raree.pdf|title=Rare Earths |publisher=United States Geological Survey|date=January 2010|access-date=2010-12-10}}</ref> Samarium is usually sold as oxide, which at the price of about US$30/kg is one of the cheapest lanthanide oxides.<ref name="price">[https://web.archive.org/web/20121014122537/http://lynascorp.com/page.asp?category_id=1&page_id=25 What are their prices?], Lynas corp.</ref> Whereas [[mischmetal]] – a mixture of rare earth metals containing about 1% of samarium – has long been used, relatively pure samarium has been isolated only recently, through [[ion exchange]] processes, [[solvent extraction]] techniques, and [[electrochemical deposition]]. The metal is often prepared by electrolysis of a molten mixture of [[samarium(III) chloride]] with [[sodium chloride]] or [[calcium chloride]]. Samarium can also be obtained by reducing its oxide with [[lanthanum]]. The product is then distilled to separate samarium (boiling point 1794&nbsp;°C) and lanthanum (b.p.&nbsp;3464&nbsp;°C).<ref name="brit" />

Very few minerals have samarium being the most dominant element. Minerals with essential (dominant) samarium include [[monazite-(Sm)]] and [[florencite-(Sm)]]. These minerals are very rare and are usually found containing other elements, usually [[cerium]] or [[neodymium]].<ref>{{Cite journal |last1=Masau |first1=M. |last2=Cerny |first2=P. |last3=Cooper |first3=M. A. |last4=Chapman |first4=R. |last5=Grice |first5=J. D. |date=2002-12-01 |title=MONAZITE-(Sm), A NEW MEMBER OF THE MONAZITE GROUP FROM THE ANNIE CLAIM #3 GRANITIC PEGMATITE, SOUTHEASTERN MANITOBA |url=http://www.canmin.org/cgi/doi/10.2113/gscanmin.40.6.1649 |journal=The Canadian Mineralogist |language=en |volume=40 |issue=6 |pages=1649–1655 |doi=10.2113/gscanmin.40.6.1649 |bibcode=2002CaMin..40.1649M |issn=0008-4476}}</ref><ref>{{Cite journal |last1=Repina |first1=S. A. |last2=Popova |first2=V. I. |last3=Churin |first3=E. I. |last4=Belogub |first4=E. V. |last5=Khiller |first5=V. V. |date=December 2011 |title=Florencite-(Sm)—(Sm,Nd)Al<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>(OH)<sub>6</sub>: a new mineral species of the alunite–jarosite group from the subpolar Urals |url=https://link.springer.com/10.1134/S1075701511070191 |journal=Geology of Ore Deposits |language=en |volume=53 |issue=7 |pages=564–574 |doi=10.1134/S1075701511070191 |bibcode=2011GeoOD..53..564R |s2cid=97229772 |issn=1075-7015}}</ref><ref>{{cite web|url=http://www.mindat.org/min-11438.html |title=Monazite-(Sm): Monazite-(Sm) mineral information and data |website=Mindat.org |access-date=2016-03-04}}</ref><ref>{{cite web|url=http://www.mindat.org/min-42495.html |title=Florencite-(Sm): Florencite-(Sm) mineral information and data |website=Mindat.org |access-date=2016-03-04}}</ref> It is also made by [[neutron capture]] by samarium-149, which is added to the [[control rod]]s of nuclear reactors. Therefore, {{sup|151}}Sm is present in spent [[nuclear fuel]] and radioactive waste.<ref name="LA2" />