Editing Xenotime

{{Short description|Phosphate mineral}}
{{Infobox mineral
| name = Xenotime
| category = [[Phosphate minerals]]
| boxwidth =
| image = Xenotime with Rutile-08-2-78ab.jpg
| imagesize   = 260px
| caption = Xenotime with [[rutile]]
| formula = YPO<sub>4</sub>
| IMAsymbol   = Xtm<ref>{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}</ref>
| strunz = 8.AD.35
| color = Brown, brownish yellow, gray
| habit = Prismatic, radial aggregates, granular
| system = [[Tetragonal]]
| class = Dipyramidal (4/mmm) <br/>[[H-M symbol]]: (4/m)
| symmetry = ''I''4<sub>1</sub>/a
| cleavage = Perfect [100]
| fracture = Uneven to splintery
| mohs = 4.5
| luster = Vitreous to resinous
| refractive = 1.720–1.815 
| birefringence = δ = 0.096
| pleochroism = Dichroic
| streak = Pale brown, yellowish or reddish, to white
| gravity = 4.4–5.1
| melt = 
| solubility =
| diaphaneity = Translucent to opaque
| other = Not radioactive or luminescent
| references = <ref name=Lost>{{cite book|ref=Fontani|last1=Fontani|first1=Marco| author-link= Marco Fontani|last2=Costa|first2=Mariagrazia|last3=Orna|first3=Virginia|title=The Lost Elements: The Periodic Table's Shadow Side|publisher=Oxford University Press|year=2014|page=73|url=https://books.google.com/books?id=Ck9jBAAAQBAJ|isbn=978-0199383-344}}</ref><ref name=Mindat>{{cite web|url=http://www.mindat.org/min-4333.html|title=Mindat database}}</ref><ref name=Webmineral>{{cite web|url=http://www.webmineral.com/data/Xenotime-%28Y%29.shtml|title=Xenotime|work=Webmineral}}</ref><ref name=Handbook>{{cite web|url=http://rruff.geo.arizona.edu/doclib/hom/xenotimey.pdf|title=Handbook of Mineralogy}}</ref>
}}

'''Xenotime''' is a [[rare-earth]] [[phosphate mineral]], the major component of which is [[yttrium]] orthophosphate ([[yttrium|Y]][[phosphorus|P]][[oxygen|O]]<sub>4</sub>). The phosphate ions are described by a tetrahedral shape and coordinate to the center Y<sup>3+</sup> metal ion in a way that closely resembles the structure of [[zircon]] (ZrSiO<sub>4</sub>).<ref>{{Cite journal |last1=Pagliaro |first1=Francesco |last2=Comboni |first2=Davide |last3=Battiston |first3=Tommaso |last4=Krüger |first4=Hannes |last5=Hejny |first5=Clivia |last6=Kahlenberg |first6=Volker |last7=Gigli |first7=Lara |last8=Glazyrin |first8=Konstantin |last9=Liermann |first9=Hanns-Peter |last10=Garbarino |first10=Gaston |last11=Gatta |first11=G. Diego |last12=Lotti |first12=Paolo |date=December 2024 |title=Comparative thermal and compressional behaviour of natural xenotime-(Y), chernovite-(Y) and monazite-(Ce) |url=https://www.cambridge.org/core/product/identifier/S0026461X24000707/type/journal_article |journal=Mineralogical Magazine |language=en |volume=88 |issue=6 |pages=682–697 |doi=10.1180/mgm.2024.70 |bibcode=2024MinM...88..682P |issn=0026-461X}}</ref> It forms a solid solution series with [[chernovite-(Y)]] ([[yttrium|Y]][[arsenic|As]][[oxygen|O]]<sub>4</sub>) and therefore may contain trace [[impurities]] of [[arsenic]], as well as [[silicon dioxide]] and [[calcium]]. Other iso-structural ions that undergo exchanges with PO<sub>4</sub> are VO<sub>4</sub> and NbO<sub>4</sub> ions, contributing to the list of possible co-occurring elements that may be in need of separation.<ref name="linkinghub.elsevier.com">{{Cite journal |last1=Hetherington |first1=Callum J. |last2=Jercinovic |first2=Michael J. |last3=Williams |first3=Michael L. |last4=Mahan |first4=Kevin |date=2008-09-15 |title=Understanding geologic processes with xenotime: Composition, chronology, and a protocol for electron probe microanalysis |url=https://linkinghub.elsevier.com/retrieve/pii/S0009254108001952 |journal=Chemical Geology |series=The role of accessory minerals in metamorphic and igneous processes |volume=254 |issue=3 |pages=133–147 |doi=10.1016/j.chemgeo.2008.05.020 |bibcode=2008ChGeo.254..133H |issn=0009-2541|url-access=subscription }}</ref> The [[rare-earth elements]] [[dysprosium]], [[erbium]], [[terbium]] and [[ytterbium]], as well as metal elements such as [[thorium]] and [[uranium]] (all replacing yttrium) are the expressive secondary components of xenotime. Due to uranium and thorium impurities, some xenotime specimens may be weakly to strongly [[radioactive]]. [[Lithiophyllite]], [[monazite]] and [[purpurite]] are sometimes grouped with xenotime in the informal "anhydrous phosphates" group. Xenotime is used chiefly as a source of yttrium and heavy [[lanthanide]] metals (dysprosium, ytterbium, erbium and gadolinium). Occasionally, [[gemstone]]s are also cut from the finest xenotime crystals.

== Etymology ==
The name ''xenotime'' is from the [[Greek language|Greek]] words {{Transliteration|grc|kenós}} ({{wikt-lang|grc|κενός}}) 'vain' and {{Transliteration|grc|timē}} ({{wikt-lang|grc|τιμή}}) 'honor', akin to 'vainglory'. It was coined by French mineralogist [[François Sulpice Beudant]] as a rebuke of another scientist, Swedish chemist [[Jöns Jacob Berzelius]], for the latter's premature claim to have found in the mineral a new [[chemical element]] (later understood to be previously discovered yttrium). The criticism was blunted, as over time ''kenotime'' was misread and misprinted ''xenotime''<ref name=Lost/><ref name=Mindat/><ref name=Handbook/> with the error suggesting the etymology {{Transliteration|grc|xénos}} ({{wikt-lang|grc|ξένος}}) + {{Transliteration|grc|timē}} ({{lang|grc|τιμή}})  as 'different honor'. Xenotime was first described for an occurrence in [[Vest-Agder]], [[Norway]] in 1824.<ref name=Mindat/>

== Properties ==
Crystallising in the [[tetragonal]] (I4<sub>1</sub>/amd) [[crystal system]], xenotime is typically translucent to opaque (rarely transparent) in shades of brown to brownish yellow (most common) but also reddish to greenish brown and gray. Xenotime has a variable [[crystal habit|habit]]: It may be prismatic (stubby or slender and elongate) with dipyramidal terminations, in radial or granular aggregates, or rosettes. A soft mineral ([[Mohs scale of mineral hardness|Mohs hardness]] 4.5), xenotime is—in comparison to most other translucent minerals—fairly dense, with a [[specific gravity]] between 4.4–5.1. Its [[Lustre (mineralogy)|lustre]], which may be vitreous to resinous, together with its crystal system, may lead to a confusion with [[zircon]] (ZrSiO<sub>4</sub>), the latter having a similar crystal structure and with which xenotime may sometimes occur.

Xenotime has two directions of perfect prismatic [[Cleavage (crystal)|cleavage]] and its [[fracture]] is uneven to irregular (sometimes splintery). It is considered brittle and its [[Streak (mineralogy)|streak]] is white. The [[refractive index]] of xenotime is 1.720–1.815 with a [[birefringence]] of 0.095 (uniaxial positive). Xenotime is [[pleochroism|dichroic]] with pink, yellow or yellowish brown seen in the extraordinary ray and brownish yellow, grayish brown or greenish brown seen in the ordinary ray. There is no reaction under [[ultraviolet]] light. While xenotime may contain significant amounts of thorium or uranium, the mineral does not undergo [[metamictization]] like [[sphene]] or zircon would.

== Occurrence ==
Occurring as a minor accessory mineral, xenotime is found in [[pegmatite]]s and other [[igneous rock]]s, as well as [[gneiss]]es rich in [[mica]] and [[quartz]]. Associated minerals include [[biotite]] and other micas, [[chlorite group]] minerals, quartz, zircon, certain [[feldspar]]s, [[analcime]], [[anatase]], [[brookite]], [[rutile]], [[siderite]] and [[apatite]]. Xenotime is also known to be [[diagenesis|diagenetic]]: It may form as minute grains or as extremely thin (less than 10 [[micrometre|μ]]) coatings on detrital zircon grains in siliciclastic [[sedimentary rock]]s. The importance of these diagenetic xenotime deposits in the [[radiometric dating]] of sedimentary rocks is only beginning to be realized.<ref>{{cite web|url=http://www.geoconferences.org/grant_reports/2002_GAC/vallini.html |title=Geoconferences (WA) Inc |access-date=January 8, 2006 |url-status=dead |archive-url=https://web.archive.org/web/20061214120750/http://www.geoconferences.org/grant_reports/2002_GAC/vallini.html |archive-date=December 14, 2006 }} Daniela Vallini</ref> The formation of uranium and lead in xenotime ores classifies xenotime as a U-Pb chronometer, meaning it can be used for geological dating using U-Th-Pb [[geochronology]] techniques.<ref>{{Cite journal |last=Rasmussen |first=Birger |date=2005-01-01 |title=Radiometric dating of sedimentary rocks: the application of diagenetic xenotime geochronology |url=https://linkinghub.elsevier.com/retrieve/pii/S0012825204000558 |journal=Earth-Science Reviews |volume=68 |issue=3 |pages=197–243 |doi=10.1016/j.earscirev.2004.05.004 |bibcode=2005ESRv...68..197R |issn=0012-8252|url-access=subscription }}</ref> The spectrometry used in geochronology necessitates larger crystals of at least 10 μm, therefore SEM imaging is applied to identify crystals that meet the appropriate dimensions. After identification, there are various spectroscopy approaches and microprobes for geochronology: SIMS, EMPA, LA-ICP-MS, and ID-TIMS. Xenotime can be found in geological formations that formed from the mid-Archean age to the Mesezoic age, so geological dating using xenotime in sedimentary rocks is extensive and a useful application.

Discovered in 1824, xenotime's type locality is [[Hidra (island)|Hidra]] (Hitterø), [[Flekkefjord]], [[Vest-Agder]], [[Norway]]. Other notable localities include: [[Arendal]] and [[Tvedestrand]], Norway; [[Novo Horizonte, São Paulo]], [[Novo Horizonte, Bahia]] and [[Minas Gerais]], [[Brazil]]; [[Madagascar]] and [[California]], [[Colorado]], [[Georgia (U.S. state)|Georgia]], [[North Carolina]] and [[New Hampshire]], [[United States]]. A new discovery of gemmy, colour change (brownish to yellow) xenotime has been reported from [[Afghanistan]] and been found in [[Pakistan]]. Due to their isostructural nature, it is common for xenotime and zircon to co-crystallize together as composites; either forming crystal twins or growths over one another.<ref name="linkinghub.elsevier.com"/> In geochemistry, it is advantageous to do on site analysis of a given ore in order to determine the identities and the percentage of its compositions. A popular method of doing so is XEOL imaging, but another method has to be applied to xenotime-zircon ores because there is no way to distinguish between the intensities and color of their respective luminescence spectra, as both have green emissions at 580&nbsp;nm. The alternative method involves [[Annealing (materials science)|annealing]] of the ore followed by Cathodluminescence (CI) imaging techniques. This technique increases the intensity of only the zircon composition, allowing for ease in analysis.<ref>{{Cite journal |last=Imashuku |first=Susumu |date=2024-07-05 |title=Distinguishing xenotime and zircon in ores and estimating the xenotime content for on-site analysis |url=https://linkinghub.elsevier.com/retrieve/pii/S1386142524003822 |journal=Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy |volume=315 |pages=124216 |doi=10.1016/j.saa.2024.124216 |pmid=38581724 |bibcode=2024AcSpA.31524216I |issn=1386-1425|doi-access=free }}</ref> North of [[Mount Funabuse]] in [[Gifu Prefecture]], [[Japan]], a notable [[basalt]]ic [[rock (geology)|rock]] is quarried at a hill called Maru-Yama: crystals of xenotime and zircon arranged in a radiating, flower-like pattern are visible in polished slices of the rock, which is known as ''[[chrysanthemum]] stone'' (translated from the [[Japanese language|Japanese]] 菊石 ''kiku-ishi''). This stone is widely appreciated in Japan for its ornamental value.

Small tonnages of xenotime sand are recovered in association with Malaysian [[tin mining]], etc. and are processed commercially. The lanthanide content is typical of "yttrium earth" minerals and runs about two-thirds yttrium, with the remainder being mostly the heavy lanthanides, where the even-numbered lanthanides (such as Gd, Dy, Er, or Yb) each being present at about the 5% level, and the odd-numbered lanthanides (such as Tb, Ho, Tm, Lu) each being present at about the 1% level. Dysprosium is usually the most abundant of the even-numbered heavies, and holmium is the most abundant of the odd-numbered heavies.  The lightest lanthanides are generally better represented in monazite while the heaviest lanthanides are in xenotime.

Xenotime ores have to undergo chemical treatments to separate the rare earth elements (RREs) that make up its composition. Firstly, leaching, or dissolving of the phosphate shell is performed using [[sulfuric acid]] (H<sub>2</sub>SO<sub>4</sub>) or [[sodium hydroxide]] (NaOH), leaving behind the mixed RREs. Various techniques can be applied next to further separate the individual elements. One is the use of [[ion exchange]] methods, which encourages different elution times for different lanthanides based on ionic bonding. The quaternary ammonium anion salt trioctyl methylammonium nitrate, or commonly referred to as [[Aliquat 336]], is used to extract the lighter REEs from the heavier REEs. Yttrium is then extracted from the heavier REEs with thiocyanate salts. The remaining heavy RREs are further separated using various treatments of Aliquat 336 and nitrate salts.<ref>{{Cite journal |last1=Xie |first1=Feng |last2=Zhang |first2=Ting An |last3=Dreisinger |first3=David |last4=Doyle |first4=Fiona |date=2014-02-01 |title=A critical review on solvent extraction of rare earths from aqueous solutions |url=https://linkinghub.elsevier.com/retrieve/pii/S0892687513003452 |journal=Minerals Engineering |volume=56 |pages=10–28 |doi=10.1016/j.mineng.2013.10.021 |bibcode=2014MiEng..56...10X |issn=0892-6875|doi-access=free }}</ref>

== See also ==
*[[List of minerals]]
*[[Rare-earth mineral]]
*[[Wakefieldite]]
*[[Xenotime-(Gd)]]

==References==
{{Reflist}}

==Further reading==
*Webster, R. (2000). ''Gems: Their sources, descriptions and identification'' (5th ed.), p.&nbsp;182. Butterworth-Heinemann, Great Britain. ISBN

==External links==
{{commons category-inline|Xenotime}}

{{Phosphate minerals}}

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[[Category:Yttrium minerals]]
[[Category:Phosphate minerals]]
[[Category:Radioactive gemstones]]
[[Category:Tetragonal minerals]]
[[Category:Minerals in space group 88]]
[[Category:Gemstones]]