Editing Caesium (section)

===Occurrence===
[[File:Pollucite-RoyalOntarioMuseum-Jan18-09.jpg|thumb|Pollucite, a caesium mineral|alt=A white mineral, from which white and pale pink crystals protrude]]
{{See also|:Category:Caesium minerals|l1=Caesium minerals}}
Caesium is a relatively rare element, estimated to average 3&nbsp;[[parts per million]] in the [[abundance of elements in Earth's crust|Earth's crust]].<ref>{{cite journal |last1=Turekian |first1=K. K. |last2=Wedepohl |first2=K. H. |title=Distribution of the elements in some major units of the Earth's crust |journal=Geological Society of America Bulletin |volume=72 |issue=2 |pages=175–192 |doi=10.1130/0016-7606(1961)72[175:DOTEIS]2.0.CO;2 |issn=0016-7606 |bibcode=1961GSAB...72..175T |year=1961 |doi-access=free}}</ref> It is the 45th most abundant element and 36th among the metals.<ref>{{Cite book |last1=Kloprogge |first1=J. Theo |url=https://books.google.com/books?id=hGa8DwAAQBAJ&dq=%2245th+most+abundant+element%22&pg=PA634 |title=The Periodic Table: Nature's Building Blocks: An Introduction to the Naturally Occurring Elements, Their Origins and Their Uses |last2=Ponce |first2=Concepcion P. |last3=Loomis |first3=Tom |date=2020-11-18 |publisher=Elsevier |isbn=978-0-12-821538-8 |language=en |access-date=16 May 2024 |archive-date=16 May 2024 |archive-url=https://web.archive.org/web/20240516231733/https://books.google.com/books?id=hGa8DwAAQBAJ&pg=PA634&dq=%2245th+most+abundant+element%22&hl=en&newbks=1&newbks_redir=0&source=gb_mobile_search&ovdme=1&sa=X&ved=2ahUKEwjc2fS_ppOGAxVP5MkDHTj0CTIQ6AF6BAgHEAM#v=onepage&q=%2245th%20most%20abundant%20element%22&f=false |url-status=live }}</ref>  Caesium is 30 times less abundant than [[rubidium]], with which it is closely associated, chemically.<ref name="USGS"/>

Due to its large [[ionic radius]], caesium is one of the "[[incompatible element]]s".<ref>{{cite web |url=http://www.asi.org/adb/02/13/02/cesium-occurrence-uses.html |title=Cesium as a Raw Material: Occurrence and Uses |first=Simon |last=Rowland |publisher=Artemis Society International |date=4 July 1998 |access-date=15 February 2010 |archive-date=8 July 2021 |archive-url=https://web.archive.org/web/20210708104437/http://www.asi.org/adb/02/13/02/cesium-occurrence-uses.html |url-status=dead }}</ref> During [[fractional crystallization (geology)|magma crystallization]], caesium is concentrated in the liquid phase and crystallizes last. Therefore, the largest deposits of caesium are zone [[pegmatite]] ore bodies formed by this enrichment process. Because caesium does not substitute for [[potassium]] as readily as rubidium does, the alkali evaporite minerals [[sylvite]] (KCl) and [[carnallite]] ({{chem|KMgCl|3|·6H|2|O}}) may contain only 0.002% caesium. Consequently, caesium is found in few minerals. Percentage amounts of caesium may be found in [[beryl]] ({{chem|Be|3|Al|2|(SiO|3|)|6}}) and [[avogadrite]] ({{chem|(K,Cs)BF|4}}), up to 15&nbsp;wt% Cs<sub>2</sub>O in the closely related mineral [[pezzottaite]] ({{chem|Cs|(Be|2|Li)|Al|2|Si|6|O|18}}), up to 8.4&nbsp;wt% Cs<sub>2</sub>O in the rare mineral [[londonite]] ({{chem|(Cs,K)Al|4|Be|4|(B,Be)|12|O|28}}), and less in the more widespread [[rhodizite]].<ref name="USGS"/> The only economically important ore for caesium is [[pollucite]] {{chem|Cs(AlSi|2|O|6|)}}, which is found in a few places around the world in zoned pegmatites, associated with the more commercially important [[lithium]] minerals, [[lepidolite]] and [[petalite]]. Within the pegmatites, the large grain size and the strong separation of the minerals results in high-grade ore for mining.<ref name="Cerny">{{cite journal |title=The Tanco Pegmatite at Bernic Lake, Manitoba: X. Pollucite |first1=Petr |last1=Černý |author-link1=Petr Černý |first2=F. M. |last2=Simpson |journal=Canadian Mineralogist |volume=16 |pages=325–333 |date=1978 |url=http://rruff.geo.arizona.edu/doclib/cm/vol38/CM38_877.pdf |archive-url=https://ghostarchive.org/archive/20221010/http://rruff.geo.arizona.edu/doclib/cm/vol38/CM38_877.pdf |archive-date=10 October 2022 |url-status=live |access-date=26 September 2010}}</ref>

The world's most significant and richest known source of caesium is the [[Tanco Mine]] at [[Bernic Lake]] in [[Manitoba]], Canada, estimated to contain 350,000&nbsp;[[tonne|metric tons]] of pollucite ore, representing more than two-thirds of the world's reserve base.<ref name="Cerny"/><ref name="USGS-Cs2"/> Although the stoichiometric content of caesium in pollucite is 42.6%, pure pollucite samples from this deposit contain only about 34% caesium, while the average content is 24&nbsp;wt%.<ref name="USGS-Cs2">{{cite web |title=Cesium |last=Polyak |first=Désirée E. |url=http://minerals.usgs.gov/minerals/pubs/commodity/cesium/mcs-2009-cesiu.pdf |archive-url=https://web.archive.org/web/20090508233834/http://minerals.usgs.gov/minerals/pubs/commodity/cesium/mcs-2009-cesiu.pdf |archive-date=8 May 2009 |url-status=live |publisher=U.S. Geological Survey |access-date=17 October 2009}}</ref> Commercial pollucite contains more than 19% caesium.<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=26 September 2010 |archive-date=21 July 2010 |archive-url=https://web.archive.org/web/20100721060544/http://pubs.er.usgs.gov/usgspubs/pp/pp820 |url-status=dead}}</ref> The [[Bikita District|Bikita]] pegmatite deposit in [[Zimbabwe]] is mined for its petalite, but it also contains a significant amount of pollucite. Another notable source of pollucite is in the [[Erongo Region|Karibib Desert]], [[Namibia]].<ref name="USGS-Cs2"/> At the present rate of world mine production of 5 to 10&nbsp;metric tons per year, reserves will last for thousands of years.<ref name="USGS"/>