Editing Rubidium (section)

==Occurrence==
Rubidium is not abundant, being one of 56 elements that combined make up 0.05% of the Earth's crust; at roughly the 23rd <!-- verified in USGS ref -->[[Abundance of elements in Earth's crust|most abundant element in the Earth's crust]] it is more abundant than [[zinc]] or [[copper]].<ref name="USGS">{{cite web |url = http://pubs.usgs.gov/of/2003/of03-045/of03-045.pdf |publisher = United States Geological Survey |access-date = 2010-12-04 |title = Mineral Commodity Profile: Rubidium |first1 = William C. |last1 = Butterman |first2 = William E. |last2 = Brooks |first3 = Robert G. Jr. |last3 = Reese |date=2003}}</ref>{{rp|4}} It occurs naturally in the minerals [[leucite]], [[pollucite]], [[carnallite]], and [[zinnwaldite]], which contain as much as 1% rubidium [[oxide]]. [[Lepidolite]] contains between 0.3% and 3.5% rubidium, and is the commercial source of the element.<ref>{{Cite journal |title =Trace element chemistry of lithium-rich micas from rare-element granitic pegmatites |volume = 55
| issue = 13 |date = 1995 |doi = 10.1007/BF01162588 |pages = 203–215 |journal = Mineralogy and Petrology |first = M. A. |last = Wise |bibcode = 1995MinPe..55..203W |s2cid = 140585007
}}</ref> Some [[potassium]] minerals and [[potassium chloride]]s also contain the element in commercially significant quantities.<ref>{{cite book |last=Norton |first=J. J. |date=1973 |chapter=Lithium, cesium, and rubidium—The rare alkali metals |editor=Brobst, D. A. |editor2=Pratt, W. P. |title=United States mineral resources |publisher=U.S. Geological Survey Professional |volume=Paper 820 |pages=365–378 |chapter-url=https://pubs.er.usgs.gov/usgspubs/pp/pp820 |access-date=2010-09-26 |archive-date=2010-07-21 |archive-url=https://web.archive.org/web/20100721060544/http://pubs.er.usgs.gov/usgspubs/pp/pp820 |url-status=dead }}</ref>

[[Seawater]] contains an average of 125&nbsp;μg/L of rubidium compared to the much higher value for potassium of 408&nbsp;mg/L and the much lower value of 0.3&nbsp;μg/L for caesium.<ref>{{cite journal |last1 = Bolter |first1 = E. |last2 = Turekian |first2 = K. |last3 = Schutz |first3 = D. |title = The distribution of rubidium, cesium and barium in the oceans |journal = Geochimica et Cosmochimica Acta |volume = 28 |issue = 9 |pages = 1459 |date = 1964 |doi = 10.1016/0016-7037(64)90161-9 |bibcode = 1964GeCoA..28.1459B }}</ref> Rubidium is the 18th most abundant element in seawater.<ref name="Hart-1973">{{Cite book |last1=Hart |first1=William A. |url=https://doi.org/10.1016/C2013-0-05695-2 |title=The Chemistry of Lithium, Sodium, Potassium, Rubidium, Cesium and Francium |last2=Beumel Jr. |first2=O.F . |last3=Whaley |first3=Thomas P. |date=1973 |publisher=Pergamon |isbn=978-0-08-018799-0|pages= |doi=10.1016/c2013-0-05695-2}}</ref>{{rp|371}}

Because of its large [[ionic radius]], rubidium is one of the "[[incompatible element]]s".<ref>{{cite book |url = https://books.google.com/books?id=385nPZOXmYAC&pg=PA224 |page = 224 |title = Cosmochemistry |isbn = 978-0-521-87862-3 |author1 = McSween Jr., Harry Y |author2 = Huss, Gary R |date = 2010|publisher = Cambridge University Press }}</ref> During [[Fractional crystallization (geology)|magma crystallization]], rubidium is concentrated together with its heavier analogue caesium in the liquid phase and crystallizes last. Therefore, the largest deposits of rubidium and caesium are zone [[pegmatite]] ore bodies formed by this enrichment process. Because rubidium substitutes for [[potassium]] in the crystallization of magma, the enrichment is far less effective than that of caesium. Zone pegmatite ore bodies containing mineable quantities of caesium as [[pollucite]] or the lithium minerals [[lepidolite]] are also a source for rubidium as a by-product.<ref name="USGS" />

Two notable sources of rubidium are the rich deposits of [[pollucite]] at [[Bernic Lake]], [[Manitoba]], Canada, and the [[rubicline]] {{chem|((Rb,K)AlSi<sub>3</sub>O<sub>8</sub>)}} found as impurities in pollucite on the Italian island of [[Elba]], with a rubidium content of 17.5%.<ref>{{Cite journal | title = Rubicline, a new feldspar from San Piero in Campo, Elba, Italy |journal = American Mineralogist |volume = 83 |issue = 11–12 Part 1 |pages = 1335–1339 |last1 = Teertstra |first1 = David K. |first2 = Petr |last2 = Cerny |first3 = Frank C. |last3 = Hawthorne |first4 = Julie |last4 = Pier |first5 = Lu-Min |last5 = Wang |first6 = Rodney C. |last6 =Ewing |date = 1998 |author-link2 = Petr Cerny|bibcode = 1998AmMin..83.1335T |doi = 10.2138/am-1998-11-1223 }}</ref> Both of those deposits are also sources of caesium.<ref>{{Cite encyclopedia |last=Enghag |first=Per |title=Rubidium and Cesium |url=https://onlinelibrary.wiley.com/doi/book/10.1002/9783527612338 |encyclopedia=Encyclopedia of the Elements|chapter = Rubidium and Caesium |publisher=Wiley |year=2004 |pages=301–313 |isbn=978-3-527-30666-4 |edition=1 |language=en |doi=10.1002/9783527612338.ch13}}</ref>