Editing Europium (section)

===Occurrence===
[[File:Monazit - Mosambik, O-Afrika.jpg|left|thumb|Monazite]]
Europium is not found in nature as a free element. Many minerals contain europium, with the most important sources being [[bastnäsite]], [[monazite]], [[xenotime]] and [[loparite-(Ce)]].<ref name="Kirk">{{cite book |doi=10.1002/0471238961.1201142019010215.a01.pub3 |chapter=Lanthanides |title=Kirk-Othmer Encyclopedia of Chemical Technology |date=2013 |last1=Bünzli |first1=Jean-Claude G. |pages=1–43 |isbn=978-0-471-48494-3 }}</ref> No europium-dominant minerals are known yet, despite a single find of a tiny possible Eu–O or Eu–O–C system phase in the Moon's regolith.{{fact|date=August 2024}}

Depletion or enrichment of europium in minerals relative to other rare-earth elements is known as the [[europium anomaly]].<ref>{{cite book|chapter-url = https://books.google.com/books?id=OmUXW8pqUe8C&pg=PA550|chapter = The Europium anomaly| pages = 550–553|title = Systematics and the properties of the lanthanides|isbn = 978-90-277-1613-2|last = Sinha|first= Shyama P.|author2 = Scientific Affairs Division, North Atlantic Treaty Organization|date = 1983| publisher=Springer }}</ref> Europium is commonly included in trace element studies in [[geochemistry]] and [[petrology]] to understand the processes that form [[igneous rocks]] (rocks that cooled from [[magma]] or [[lava]]). The nature of the europium anomaly found helps reconstruct the relationships within a suite of igneous rocks. The [[Abundance of elements in Earth's crust|median crustal abundance]] of europium is 2 ppm; values of the less abundant elements may vary with location by several orders of magnitude.<ref name=CRC>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> 

Divalent europium (Eu<sup>2+</sup>) in small amounts is the activator of the bright blue [[fluorescence]] of some samples of the mineral [[fluorite]] (CaF<sub>2</sub>). The reduction from Eu<sup>3+</sup> to Eu<sup>2+</sup> is induced by irradiation with energetic particles.<ref>{{cite journal|doi = 10.1007/BF00308116|title = Color centers, associated rare-earth ions and the origin of coloration in natural fluorites|date = 1978|last1 = Bill|first1 = H.|last2 = Calas|first2 = G.|journal = Physics and Chemistry of Minerals|volume = 3|issue = 2|pages = 117–131|bibcode=1978PCM.....3..117B|s2cid = 93952343}}</ref> The most outstanding examples of this originated around [[Weardale]] and adjacent parts of northern England; it was the fluorite found here that fluorescence was named after in 1852, although it was not until much later that europium was determined to be the cause.<ref>{{Cite journal|author=Allen, Robert D. |url=http://www.minsocam.org/ammin/AM37/AM37_910.pdf|title=Variations in chemical and physical properties of fluorite|journal=Am. Mineral.|volume=37|pages=910–30|year=1952}}</ref><ref>{{cite journal |last1=Valeur |first1=Bernard |last2=Berberan-Santos |first2=Mário N. |title=A Brief History of Fluorescence and Phosphorescence before the Emergence of Quantum Theory |journal=Journal of Chemical Education |date=June 2011 |volume=88 |issue=6 |pages=731–738 |doi=10.1021/ed100182h |bibcode=2011JChEd..88..731V }}</ref><ref>{{cite journal |last1=Mariano |first1=A.N |last2=King |first2=P.J |title=Europium-activated cathodoluminescence in minerals |journal=Geochimica et Cosmochimica Acta |date=May 1975 |volume=39 |issue=5 |pages=649–660 |doi=10.1016/0016-7037(75)90008-3 |bibcode=1975GeCoA..39..649M }}</ref><ref>{{cite journal |last1=Przibram |first1=K. |title=Fluorescence of Fluorite and the Bivalent Europium Ion |journal=Nature |date=January 1935 |volume=135 |issue=3403 |pages=100 |doi=10.1038/135100a0 |bibcode=1935Natur.135..100P }}</ref>

In [[astrophysics]], the signature of europium in stellar [[spectroscopy|spectra]] can be used to [[Stellar classification|classify stars]] and inform theories of how or where a particular star was born. For instance, astronomers used the relative levels of europium to iron within the star [[LAMOST J112456.61+453531.3]] to propose that the accretion process for star occurred late.<ref>{{cite journal |last1=Xing |first1=Qian-Fan |last2=Zhao |first2=Gang |last3=Aoki |first3=Wako |last4=Honda |first4=Satoshi |last5=Li |first5=Hai-Ning |last6=Ishigaki |first6=Miho N. |last7=Matsuno |first7=Tadafumi |date=29 April 2019 |title=Evidence for the accretion origin of halo stars with an extreme r-process enhancement |journal=[[Nature (journal)|Nature]] |volume= 3|issue= 7|pages= 631–635|doi=10.1038/s41550-019-0764-5 |bibcode=2019NatAs...3..631X |arxiv=1905.04141 |s2cid=150373875 }}</ref>