Editing Apatite

{{short description|Mineral group, calcium phosphate}}
{{distinguish|appetite}}

{{Infobox mineral
| name        = Apatite group
| category    = [[Phosphate mineral]]
| boxwidth    =
| image       = Apatite Canada.jpg
| caption     = Apatite (CaF) (fluorapatite) doubly-terminated crystal in calcite
| formula     = Ca<sub>5</sub>(PO<sub>4</sub>)<sub>3</sub>(F,Cl,OH)
|IMAsymbol=Ap<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>
| molweight   =
| strunz      = 8.BN.05
| color       = [[transparency (optics)|Transparent]] to translucent, usually green, less often colorless, yellow, blue to violet, pink, brown.<ref name="GRG">[[Gemological Institute of America]], ''GIA Gem Reference Guide'' 1995, {{ISBN|0-87311-019-6}}</ref>
| habit       = Tabular, prismatic crystals, massive, compact or granular
| system      = [[Hexagonal (crystal system)|Hexagonal]]
| class       = Dipyramidal (6/m) <br /><small>(same [[H-M symbol]])</small><ref name=Webmineral>[http://webmineral.com/data/Apatite.shtml Apatite]. Webmineral</ref>
| symmetry    = ''P6<sub>3</sub>/m'' (no. 176)
| twinning    =
| cleavage    = [0001] indistinct, [1010] indistinct<ref name=Webmineral/>
| fracture    = Conchoidal to uneven<ref name="GRG"/>
| mohs        = 5<ref name="GRG"/> (defining mineral)
| luster      = Vitreous<ref name="GRG"/> to subresinous
| polish      = Vitreous<ref name="GRG"/>
| refractive  = 1.634–1.638 (+0.012, −0.006)<ref name="GRG"/>
| opticalprop = Double refractive, uniaxial negative<ref name="GRG"/>
| birefringence = 0.002–0.008<ref name="GRG"/>
| dispersion  = 0.013<ref name="GRG"/>
| pleochroism = ''Blue stones'' – strong, blue and yellow to colorless. Other colors are weak to very weak.<ref name="GRG"/>
| fluorescence= ''Yellow stones'' – purplish-pink, which is stronger in long wave; ''blue stones''&nbsp;– blue to light-blue in both long and short wave; ''green stones''&nbsp;– greenish-yellow, which is stronger in long wave; ''violet stones''&nbsp;– greenish-yellow in long wave, light-purple in short wave.<ref name="GRG"/>
| absorption  =
| streak      = White
| gravity     = 3.16–3.22<ref name=Webmineral/>
| density     =
| melt        =
| fusibility  =
| diagnostic  =
| solubility  =
| diaphaneity = Transparent to translucent<ref name=Webmineral/>
| other       =
}}

'''Apatite''' is a group of [[phosphate minerals]], usually [[hydroxyapatite]], [[fluorapatite]] and chlorapatite, with high concentrations of [[Hydroxide|OH]]<sup>−</sup>, [[Fluoride|F]]<sup>−</sup> and [[Chloride|Cl]]<sup>−</sup> [[ion]], respectively, in the [[crystal]]. The formula of the admixture of the three most common [[Endmember (mineralogy)|endmembers]] is written as [[Calcium|Ca]]<sub>10</sub>([[Phosphate|PO<sub>4</sub>]])<sub>6</sub>(OH,F,Cl)<sub>2</sub>, and the crystal unit cell formulae of the individual [[mineral]]s are written as Ca<sub>10</sub>(PO<sub>4</sub>)<sub>6</sub>(OH)<sub>2</sub>, Ca<sub>10</sub>(PO<sub>4</sub>)<sub>6</sub>F<sub>2</sub> and Ca<sub>10</sub>(PO<sub>4</sub>)<sub>6</sub>Cl<sub>2</sub>.

The mineral was named apatite by the German [[geologist]] [[Abraham Gottlob Werner]] in 1786,<ref>According to Werner himself – (Werner, 1788), p. 85 – the name "apatite" first appeared in print in:
*  Gerhard, C.A., ''Grundriss des Mineral-systems'' [Outline of the system of minerals] (Berlin, (Germany):  Christian Friedrich Himburg, 1786), [https://books.google.com/books?id=DRI-AAAAcAAJ&pg=PA281 p. 281.] From p. 281: ''"Von einigen noch nicht genau bestimmten und ganz neu entdeckten Mineralien. Ich rechne hierzu folgende drei Körper: 1. Den Apatit des Herrn Werners. … "''(On some still not precisely determined and quite recently discovered minerals. I count among these the following three substances: 1. the apatite of Mr. Werner. … )
Werner described the mineral in some detail in an article of 1788.
* Werner, A.G. (1788) [https://books.google.com/books?id=XyU7AAAAcAAJ&pg=PA76 "Geschichte, Karakteristik, und kurze chemische Untersuchung des Apatits"] (History, characteristics, and brief chemical investigation of apatite), ''Bergmännisches Journal'' (Miners' Journal), vol. 1, pp. 76–96. [https://books.google.com/books?id=XyU7AAAAcAAJ&pg=PA84 On pp. 84–85], Werner explained that because mineralogists had repeatedly misclassified it (e.g., as [[Beryl#Aquamarine and maxixe|aquamarine]]), he gave apatite the name of "deceiver": ''"Ich wies hierauf diesem Foßile, als einer eigenen Gattung, sogleich eine Stelle in dem Kalkgeschlechte an; und ertheilte ihm, – weil es bisher alle Mineralogen in seiner Bestimmung irre geführt hatte, – den Namen ''Apatit'', den ich von dem griechischen Worte ''απατάω'' (decipio) bildete, und welcher so viel as ''Trügling'' sagt."'' (I then immediately assigned to this fossil [i.e., material obtained from underground], as a separate type, a place in the lime lineage; and conferred on it – because it had previously led astray all mineralogists in its classification – the name "apatite", which I formed from the Greek word ''απατάω'' [apatáō] (I deceive) and which says as much as [the word] "deceiver".)</ref> although the specific mineral he had described was reclassified as fluorapatite in 1860 by the German [[mineralogist]] [[Karl Friedrich August Rammelsberg]]. Apatite is often mistaken for other minerals. This tendency is reflected in the mineral's name, which is derived from the Greek word ἀπατάω (apatáō), which means ''to deceive''.<ref>{{Cite web |title=ἀπατάω |url=https://logeion.uchicago.edu/%E1%BC%80%CF%80%CE%B1%CF%84%CE%AC%CF%89 |url-status=live |archive-url=https://web.archive.org/web/20230222133315/https://logeion.uchicago.edu/%E1%BC%80%CF%80%CE%B1%CF%84%CE%AC%CF%89 |archive-date=Feb 22, 2023 |access-date=Feb 22, 2023 |website=[[Logeion]]}}</ref><ref>{{cite web|url=http://www.mindat.org/min-1572.html |title=Fluorapatite mineral information and data |website=mindat.org |access-date=30 January 2018}}</ref>

==Geology==
Apatite is very common as an [[accessory mineral]] in [[igneous]] and [[metamorphic]] rocks, where it is the most common [[phosphate mineral]]. However, occurrences are usually as small grains which are often visible only in [[thin section]]. Coarsely crystalline apatite is usually restricted to [[pegmatites]], [[gneiss]] derived from [[sediments]] rich in [[carbonate minerals]], [[skarn]]s, or [[marble]]. Apatite is also found in [[clastic]] [[sedimentary rock]] as grains eroded out of the source rock.<ref name=Nesse349>{{cite book |last1=Nesse |first1=William D. |title=Introduction to mineralogy |date=2000 |publisher=Oxford University Press |location=New York |isbn=9780195106916 |page=349}}</ref><ref>[https://www.minerals.net/mineral/apatite.aspx The Apatite Mineral Group]. minerals.net.  Retrieved on 2020-10-14.</ref> [[Phosphorite]] is a phosphate-rich [[sedimentary rock]] containing as much as 80% apatite,<ref>{{cite journal |last1=Gulbrandsen |first1=R.A |title=Chemical composition of phosphorites of the Phosphoria Formation |journal=Geochimica et Cosmochimica Acta |date=August 1966 |volume=30 |issue=8 |pages=769–778 |doi=10.1016/0016-7037(66)90131-1|bibcode=1966GeCoA..30..769G }}</ref> which is present as [[cryptocrystalline]] masses referred to as ''collophane''.<ref>{{cite journal |last1=Burnett |first1=William C. |title=Geochemistry and origin of phosphorite deposits from off Peru and Chile |journal=GSA Bulletin |date=1 June 1977 |volume=88 |issue=6 |pages=813–823 |doi=10.1130/0016-7606(1977)88<813:GAOOPD>2.0.CO;2|bibcode=1977GSAB...88..813B }}</ref> Economic quantities of apatite are also sometimes found in [[nepheline syenite]] or in [[carbonatite]]s.<ref name=Nesse349/>

Apatite is the defining mineral for 5 on the [[Mohs scale of mineral hardness|Mohs scale]].{{sfn|Nesse|2000|p=99}} It can be distinguished [[Field work|in the field]] from [[beryl]] and [[tourmaline]] by its relative softness. It is often fluorescent under [[ultraviolet light]].<ref>{{cite book |last1=Sinkankas |first1=John |title=Mineralogy for amateurs. |date=1964 |publisher=Van Nostrand |location=Princeton, N.J. |isbn=0442276249 |pages=417–418}}</ref>

Apatite is one of a few minerals produced and used by biological micro-environmental systems.<ref name=Nesse349/> Hydroxyapatite (IMA name: Hydroxylapatite), is the major component of [[tooth enamel]] and [[bone mineral]]. A relatively rare form of apatite in which most of the OH groups are absent and containing many [[carbonate]] and acid phosphate substitutions is a large component of [[bone]] material.<ref>{{cite journal |last1=Combes |first1=Christèle |last2=Cazalbou |first2=Sophie |last3=Rey |first3=Christian |title=Apatite Biominerals |journal=Minerals |date=5 April 2016 |volume=6 |issue=2 |pages=34 |doi=10.3390/min6020034|bibcode=2016Mine....6...34C |doi-access=free }}</ref>

Fluorapatite (or fluoroapatite) is more resistant to acid attack than is hydroxyapatite; in the mid-20th century, it was discovered that communities whose water supply naturally contained fluorine had lower rates of [[dental caries]].<ref name=NICDR>{{cite web |url=http://www.nidcr.nih.gov/OralHealth/Topics/Fluoride/TheStoryofFluoridation.htm |title=The story of fluoridation |publisher=National Institute of Dental and Craniofacial Research |date=2008-12-20 }}</ref> [[Fluoridated water]] allows exchange in the [[tooth|teeth]] of fluoride ions for [[Hydroxyl#Hydroxyl group|hydroxyl groups]] in apatite. Similarly, toothpaste typically contains a source of fluoride [[anions]] (e.g. sodium fluoride, [[sodium monofluorophosphate]]). Too much fluoride results in [[dental fluorosis]] and/or [[skeletal fluorosis]].<ref name=FRWG>{{cite journal | title = Recommendations for using fluoride to prevent and control dental caries in the United States. Centers for Disease Control and Prevention | journal = MMWR. Recommendations and Reports | volume = 50 | issue = RR-14 | pages = 1–42 | date = August 2001 | pmid = 11521913 | url = http://cdc.gov/mmwr/preview/mmwrhtml/rr5014a1.htm}}
*{{cite web |date=2007-08-09 |title=CDC Releases New Guidelines on Fluoride Use to Prevent Tooth Decay |website=Centers for Disease Control and Prevention |url=http://cdc.gov/fluoridation/guidelines/tooth_decay.htm |archive-url=https://web.archive.org/web/20080308203450/https://cdc.gov/fluoridation/guidelines/tooth_decay.htm |archive-date=2008-03-08}}</ref>

[[Fission track dating|Fission tracks]] in apatite are commonly used to determine the thermal histories of [[orogenic belt]]s and of [[Sedimentary rock|sediments]] in [[sedimentary basin]]s.<ref>{{Cite book|date=2019|editor-last=Malusà|editor-first=Marco G.|editor2-last=Fitzgerald|editor2-first=Paul G.|title=Fission-Track Thermochronology and its Application to Geology|series=Springer Textbooks in Earth Sciences, Geography and Environment |publisher=Springer Textbooks in Earth Sciences, Geography and Environment|doi=10.1007/978-3-319-89421-8|issn=2510-1307|isbn=978-3-319-89419-5|s2cid=146467911}}</ref> [[Helium dating|(U-Th)/He dating]] of apatite is also well established from noble gas diffusion studies<ref>{{Cite journal|last1=Zeitler|first1=P.K.|last2=Herczeg|first2=A.L.|last3=McDougall|first3=I.|last4=Honda|first4=M.|date=October 1987|title=U-Th-He dating of apatite: A potential thermochronometer|journal=Geochimica et Cosmochimica Acta|volume=51|issue=10|pages=2865–2868|doi=10.1016/0016-7037(87)90164-5|issn=0016-7037|bibcode=1987GeCoA..51.2865Z}}</ref><ref>{{Cite journal|last1=Wolf|first1=R.A.|last2=Farley|first2=K.A.|last3=Silver|first3=L.T.|date=November 1996|title=Helium diffusion and low-temperature thermochronometry of apatite|journal=Geochimica et Cosmochimica Acta|volume=60|issue=21|pages=4231–4240|doi=10.1016/s0016-7037(96)00192-5|issn=0016-7037|bibcode=1996GeCoA..60.4231W}}</ref><ref>{{Cite journal|last1=Warnock|first1=A.C.|last2=Zeitler|first2=P.K.|last3=Wolf|first3=R.A.|last4=Bergman|first4=S.C.|date=December 1997|title=An evaluation of low-temperature apatite U Th/He thermochronometry|journal=Geochimica et Cosmochimica Acta|volume=61|issue=24|pages=5371–5377|doi=10.1016/s0016-7037(97)00302-5|issn=0016-7037|bibcode=1997GeCoA..61.5371W}}</ref><ref>{{Cite journal|last=Farley|first=K. A.|date=2000-02-10|title=Helium diffusion from apatite: General behavior as illustrated by Durango fluorapatite|journal=Journal of Geophysical Research: Solid Earth|volume=105|issue=B2|pages=2903–2914|doi=10.1029/1999jb900348|issn=0148-0227|bibcode=2000JGR...105.2903F|url=https://authors.library.caltech.edu/37451/1/1999JB900348.pdf|doi-access=free}}</ref><ref>{{Cite journal|last1=Shuster|first1=David L.|last2=Flowers|first2=Rebecca M.|last3=Farley|first3=Kenneth A.|date=September 2006|title=The influence of natural radiation damage on helium diffusion kinetics in apatite|journal=Earth and Planetary Science Letters|volume=249|issue=3–4|pages=148–161|doi=10.1016/j.epsl.2006.07.028|issn=0012-821X|bibcode=2006E&PSL.249..148S}}</ref><ref>{{Cite journal|last1=Idleman|first1=Bruce D.|last2=Zeitler|first2=Peter K.|last3=McDannell|first3=Kalin T.|date=January 2018|title=Characterization of helium release from apatite by continuous ramped heating|journal=Chemical Geology|volume=476|pages=223–232|doi=10.1016/j.chemgeo.2017.11.019|issn=0009-2541|bibcode=2018ChGeo.476..223I}}</ref><ref>{{Cite journal|last1=McDannell|first1=Kalin T.|last2=Zeitler|first2=Peter K.|last3=Janes|first3=Darwin G.|last4=Idleman|first4=Bruce D.|last5=Fayon|first5=Annia K.|date=February 2018|title=Screening apatites for (U-Th)/He thermochronometry via continuous ramped heating: He age components and implications for age dispersion|journal=Geochimica et Cosmochimica Acta|volume=223|pages=90–106|doi=10.1016/j.gca.2017.11.031|issn=0016-7037|bibcode=2018GeCoA.223...90M}}</ref> for use in determining thermal histories<ref>{{Cite journal|last1=House|first1=M.A.|last2=Wernicke|first2=B.P.|last3=Farley|first3=K.A.|last4=Dumitru|first4=T.A.|date=October 1997|title=Cenozoic thermal evolution of the central Sierra Nevada, California, from (UTh)/He thermochronometry|journal=Earth and Planetary Science Letters|volume=151|issue=3–4|pages=167–179|doi=10.1016/s0012-821x(97)81846-8|issn=0012-821X}}</ref><ref>{{Cite journal|last1=Ehlers|first1=Todd A.|last2=Farley|first2=Kenneth A.|date=January 2003|title=Apatite (U–Th)/He thermochronometry: methods and applications to problems in tectonic and surface processes|journal=Earth and Planetary Science Letters|volume=206|issue=1–2|pages=1–14|doi=10.1016/s0012-821x(02)01069-5|issn=0012-821X|bibcode=2003E&PSL.206....1E}}</ref> and other, less typical applications such as paleo-wildfire dating.<ref>{{Cite journal|last1=Reiners|first1=P. W.|last2=Thomson|first2=S. N.|last3=McPhillips|first3=D.|last4=Donelick|first4=R. A.|last5=Roering|first5=J. J.|date=2007-10-12|title=Wildfire thermochronology and the fate and transport of apatite in hillslope and fluvial environments|journal=Journal of Geophysical Research|volume=112|issue=F4|pages=F04001|doi=10.1029/2007jf000759|issn=0148-0227|bibcode=2007JGRF..112.4001R|doi-access=free}}</ref>

==Uses==
The primary use of apatite is as a source of phosphate in the manufacture of [[fertilizer]] and in other industrial uses. It is occasionally used as a gemstone.{{sfn|Nesse|2000|pp=348–49}} Ground apatite was used as a pigment for the [[Terracotta Army]] of 3rd-century BCE China,<ref>{{cite journal |last1=Herm |first1=C. |last2=Thieme |first2=C. |last3=Emmerling |first3=E. |last4=Wu |first4=Y.Q. |last5=Zhou |first5=T. |last6=Zhang |first6=Z. |year=1995 |title=Analysis of painting materials of the polychrome terracotta army of the first Emperor Qin Shi Huang |journal=Arbeitsheft des Bayerischen Landesamtes für Denkmalpflege |pages=675–84 |url=https://www.researchgate.net/publication/333317547 |access-date=30 July 2021}}</ref> and in [[Qing dynasty]] [[Vitreous enamel|enamel]] for [[metalware]].<ref>{{cite journal |last1=Colomban |first1=Philippe |last2=Kırmızı |first2=Burcu |last3=Zhao |first3=Bing |last4=Clais |first4=Jean-Baptiste |last5=Yang |first5=Yong |last6=Droguet |first6=Vincent |title=Non-Invasive On-Site Raman Study of Pigments and Glassy Matrix of 17th–18th Century Painted Enamelled Chinese Metal Wares: Comparison with French Enamelling Technology |journal=Coatings |date=12 May 2020 |volume=10 |issue=5 |pages=471 |doi=10.3390/coatings10050471|doi-access=free }}</ref>

During digestion of apatite with [[sulfuric acid]] to make [[phosphoric acid]], [[hydrogen fluoride]] is produced as a byproduct from any [[fluorapatite]] content. This byproduct is a minor industrial source of [[hydrofluoric acid]].<ref>{{cite journal|last1=Villalba|first1=Gara|last2=Ayres|first2=Robert U.|last3=Schroder|first3=Hans|year=2008|title=Accounting for Fluorine: Production, Use, and Loss|journal=Journal of Industrial Ecology|volume=11|pages=85–101|doi=10.1162/jiec.2007.1075|s2cid=153740615}}<!--|access-date=2011-05-07--></ref> Apatite is also occasionally a source of [[uranium]] and [[vanadium]], present as trace elements in the mineral.{{sfn|Nesse|2000|pp=348–49}}

Fluoro-chloro apatite forms the basis of the now obsolete halophosphor [[fluorescent lamp|fluorescent tube]] phosphor system. [[Dopant]] elements of manganese and antimony, at less than one mole-percent — in place of the calcium and phosphorus — impart the fluorescence, and adjustment of the fluorine-to-chlorine ratio alter the shade of white produced. This system has been almost entirely replaced by the [[fluorescent lamp#Phosphor Composition|tri-phosphor]] system.<ref>Henderson and Marsden, "Lamps and Lighting", Edward Arnold Ltd., 1972, {{ISBN|0-7131-3267-1}}</ref>

Apatites are also a proposed host material for storage of [[nuclear waste]], along with other phosphates.<ref>{{cite journal |last1=Oelkers |first1=E. H. |last2=Montel |first2=J.-M. |title=Phosphates and Nuclear Waste Storage |journal=Elements |date=1 April 2008 |volume=4 |issue=2 |pages=113–16 |doi=10.2113/GSELEMENTS.4.2.113|bibcode=2008Eleme...4..113O }}</ref><ref>{{cite journal |last1=Ewing |first1=R. C. |last2=Wang |first2=L. |title=Phosphates as Nuclear Waste Forms |journal=Reviews in Mineralogy and Geochemistry |date=1 January 2002 |volume=48 |issue=1 |pages=67399 |doi=10.2138/rmg.2002.48.18|bibcode=2002RvMG...48..673E }}</ref><ref>{{cite journal |last1=Rigali |first1=Mark J. |last2=Brady |first2=Patrick V. |last3=Moore |first3=Robert C. |title=Radionuclide removal by apatite |journal=American Mineralogist |date=December 2016 |volume=101 |issue=12 |pages=2611–19 |doi=10.2138/am-2016-5769|bibcode=2016AmMin.101.2611R |osti=1347532 |s2cid=133276331 }}</ref>

===Gemology===
[[File:Apatite taillée.jpg|thumb|left|Faceted blue apatite, Brazil]]
Apatite is infrequently used as a [[gemstone]]. [[Transparency (optics)|Transparent]] stones of clean color have been faceted, and [[chatoyant]] specimens have been [[cabochon]]-cut.<ref name="GRG"/> Chatoyant stones are known as ''cat's-eye apatite'',<ref name="GRG"/> transparent green stones are known as ''asparagus stone'',<ref name="GRG"/> and blue stones have been called ''moroxite''.<ref>Streeter, Edwin W., [http://www.farlang.com/gemstones/streeter-precious-stones/page_306 Precious Stones and Gems] 6th edition, George Bell and Sons, London, 1898, p. 306</ref> If crystals of [[rutile]] have grown in the crystal of apatite, in the right light the cut stone displays a cat's-eye effect.  Major sources for gem apatite are<ref name="GRG"/> Brazil, Myanmar, and Mexico. Other sources include<ref name="GRG"/> Canada, Czech Republic, Germany, India, Madagascar, Mozambique, Norway, South Africa, Spain, Sri Lanka, and the United States.

=== Use as an ore mineral ===
[[File:Thin section microscopy Siilinjärvi R301 6170 apatite.jpg|thumb|Apatite in [[Optical mineralogy|photomicrographs]] of a thin section from the [[Siilinjärvi apatite mine]]. In cross-polarized light on left, plane-polarized light on right.]]
[[File:Siilinjärvi Särkijärvi pit.jpg|thumb|An apatite mine in [[Siilinjärvi]], Finland.]]
Apatite is occasionally found to contain significant amounts of [[rare-earth elements]] and can be used as an [[ore]] for those metals.<ref>Salvi S, Williams-Jones A. 2004. Alkaline granite-syenite deposits. In Linnen RL, Samson IM, editors. Rare element geochemistry and mineral deposits. St. Catharines (ON): Geological Association of Canada. pp. 315–41 {{ISBN|1-897095-08-2}}</ref>  This is preferable to traditional [[Rare-earth mineral|rare-earth ores]] such as [[monazite]],<ref>Haxel G, Hedrick J, Orris J. 2006. [http://pubs.usgs.gov/fs/2002/fs087-02/fs087-02.pdf Rare earth elements critical resources for high technology]. Reston (VA): United States Geological Survey. USGS Fact Sheet: 087-02.</ref> as apatite is not very radioactive and does not pose an [[environmental hazard]] in [[mine tailings]].
However, apatite often contains [[uranium]] and its equally radioactive [[decay chain|decay-chain]] nuclides.<ref>{{Cite web|url=https://pubs.usgs.gov/bul/1009f/report.pdf|title=Glossary of Uranium- and Thorium-Bearing Minerals (Third Edition) |author=U. S. Atomic Energy Commission}}</ref>

The town of [[Apatity]] in the Arctic North of Russia was named for its mining operations for these ores.

Apatite is an ore mineral at the [[Hoidas Lake]] rare-earth project.<ref>[http://www.gwmg.ca/projects/hoidas-lake Great Western Minerals Group Ltd. | Projects – Hoidas Lake, Saskatchewan] {{Webarchive|url=https://web.archive.org/web/20080701015402/http://www.gwmg.ca/projects/hoidas-lake |date=2008-07-01 }}. Gwmg.ca (2010-01-27). Retrieved on 2011-07-24.</ref>

==Thermodynamics==
The [[Standard enthalpy of formation|standard enthalpies of formation]] in the crystalline state of hydroxyapatite, chlorapatite and a preliminary value for bromapatite, have been determined by reaction-solution [[calorimetry]]. Speculations on the existence of a possible fifth member of the calcium apatites family, iodoapatite, have been drawn from energetic considerations.<ref>{{cite journal|doi=10.1016/j.jct.2005.01.010 |author1=Cruz, F.J.A.L. |author2=Minas da Piedade, M.E. |author3=Calado, J.C.G. |title=Standard molar enthalpies of formation of hydroxy-, chlor-, and bromapatite |journal=J. Chem. Thermodyn. |volume=37 |year=2005 |pages=1061–70|issue=10|bibcode=2005JChTh..37.1061C }}</ref>

Structural and [[Thermodynamics|thermodynamic]] properties of crystal hexagonal calcium apatites, Ca<sub>10</sub>(PO<sub>4</sub>)<sub>6</sub>(X)<sub>2</sub> (X= OH, F, Cl, Br), have been investigated using an all-atom Born-Huggins-Mayer potential<ref>See:  [http://www.sklogwiki.org/SklogWiki/index.php/Born-Huggins-Meyer_potential Born-Huggins-Mayer potential (SklogWiki)]</ref> by a [[molecular dynamics]] technique. The accuracy of the model at room temperature and atmospheric pressure was checked against crystal structural data, with maximum deviations of c. 4% for the haloapatites and 8% for hydroxyapatite. High-pressure simulation runs, in the range 0.5–75 kbar, were performed in order to estimate the isothermal compressibility coefficient of those compounds. The deformation of the compressed solids is always elastically anisotropic, with BrAp exhibiting a markedly different behavior from those displayed by HOAp and ClAp. High-pressure p-V data were fitted to the Parsafar-Mason equation of state<ref>Parsafar, Gholamabbas and Mason, E.A. (1994) "Universal equation of state for compressed solids," ''Physical Review B Condensed Matter'', '''49''' (5)  :  3049–60.</ref> with an accuracy better than 1%.<ref>{{cite journal|doi=10.1021/jp054304p |pmid=16375450 |author1=Cruz, F.J.A.L. |author2=Canongia Lopes, J.N. |author3=Calado, J.C.G. |author4=Minas da Piedade, M.E. |title=A Molecular Dynamics Study of the Thermodynamic Properties of Calcium Apatites. 1. Hexagonal Phases |journal=J. Phys. Chem. B |volume=109 |year=2005 |pages=24473–79|issue=51}}</ref>

The monoclinic solid phases Ca<sub>10</sub>(PO<sub>4</sub>)<sub>6</sub>(X)<sub>2</sub> (X= OH, Cl) and the molten hydroxyapatite compound have also been studied by molecular dynamics.<ref>{{cite journal|doi=10.1021/jp055808q |pmid=16509739 |author1=Cruz, F.J.A.L. |author2=Canongia Lopes, J.N. |author3=Calado, J.C.G. |title=Molecular Dynamics Study of the Thermodynamic Properties of Calcium Apatites. 2. Monoclinic Phases |journal=J. Phys. Chem. B |volume=110 |year=2006 |pages=4387–92|issue=9}}</ref><ref>{{cite journal|doi=10.1016/j.fluid.2005.12.021 |author1=Cruz, F.J.A.L. |author2=Canongia Lopes, J.N. |author3=Calado, J.C.G. |title=Molecular dynamics simulations of molten calcium hydroxyapatite |journal=Fluid Phase Eq. |volume=241 |year=2006 |pages=51–58|issue=1–2|bibcode=2006FlPEq.241...51C }}</ref>

==Lunar science==
[[Moon rocks]] collected by astronauts during the [[Apollo program]] contain traces of apatite.<ref>{{cite journal|author=Smith, J. V.|author2=Anderson, A. T.|author3=Newton, R. C.|author4=Olsen, E. J.|author5=Crewe, A. V.|author6=Isaacson, M. S. |title=Petrologic history of the moon inferred from petrography, mineralogy and petrogenesis of Apollo 11 rocks | bibcode=1970GeCAS...1..897S |journal=Geochimica et Cosmochimica Acta |volume=34, Supplement 1 |year=1970 |pages=897–925 | doi = 10.1016/0016-7037(70)90170-5 }}</ref> Following new insights about the presence of water in the moon,<ref>{{cite journal|doi=10.1038/nature07047|author1=Saal, Alberto E. |author2=Hauri, Erik H. |author3=Cascio, Mauro L. |author4=Van Orman, James A. |author5=Rutherford, Malcolm C. |author6=Cooper, Reid F. |title=Volatile content of lunar volcanic glasses and the presence of water in the Moon's interior|year=2008|journal=Nature|volume=454|issue=7201 |pages=192–195|pmid=18615079 |bibcode=2008Natur.454..192S |s2cid=4394004 }}</ref> re-analysis of these samples in 2010 revealed water trapped in the mineral as [[hydroxyl]], leading to estimates of water on the lunar surface at a rate of at least 64 parts per billion{{snd}}100 times greater than previous estimates{{snd}}and as high as 5 parts per million.<ref>{{cite journal|doi=10.1073/pnas.1006677107 |author1=McCubbin, Francis M. |author2=Steele, Andrew |author3=Haurib, Erik H. |author4=Nekvasilc, Hanna |author5=Yamashitad, Shigeru |author6=Russell J. Hemleya |title=Nominally hydrous magmatism on the Moon|year=2010|journal=Proceedings of the National Academy of Sciences|volume=107|issue=25|pages=11223–28|bibcode = 2010PNAS..10711223M |pmid=20547878 |pmc=2895071|doi-access=free }}</ref>  If the minimum amount of mineral-locked water was hypothetically converted to liquid, it would cover the Moon's surface in roughly one meter of water.<ref>[https://web.archive.org/web/20100617184514/http://news.nationalgeographic.com/news/2010/06/100614-moon-water-hundred-lunar-proceedings-science Fazekas, Andrew "Moon Has a Hundred Times More Water Than Thought" National Geographic News (June 14, 2010)]. News.nationalgeographic.com (2010-06-14). Retrieved on 2011-07-24.</ref>

==Bio-leaching==
The [[ectomycorrhizal fungi]] ''[[Suillus granulatus]]'' and ''[[Paxillus involutus]]'' can release elements from apatite. Release of phosphate from apatite is one of the most important activities of mycorrhizal fungi,<ref>{{cite journal|url=http://mic.sgmjournals.org/content/156/3/609.full|title=Metals, minerals and microbes: geomicrobiology and bioremediation|journal=Microbiology|author1-link=Geoffrey Michael Gadd|author=Geoffrey Michael Gadd|volume=156|issue=Pt 3|date=March 2010|pages=609–43|doi=10.1099/mic.0.037143-0|pmid=20019082|doi-access=free}}</ref> which increase phosphorus uptake in plants.<ref>{{cite journal |last1=George |first1=Eckhard |last2=Marschner |first2=Horst |last3=Jakobsen |first3=Iver |title=Role of Arbuscular Mycorrhizal Fungi in Uptake of Phosphorus and Nitrogen From Soil |journal=Critical Reviews in Biotechnology |date=January 1995 |volume=15 |issue=3–4 |pages=257–70 |doi=10.3109/07388559509147412}}</ref>

== Apatite group and supergroup ==
Apatite is the prototype of a class of chemically, stoichometrically or structurally similar minerals, biological materials, and synthetic chemicals.<ref>[https://www.tomshardware.com/news/lk-99-patent-update-suggest-it-could-work J.C. Elliott, Structure and Chemistry of the Apatites and Other Calcium Orthophosphates (1994)]</ref> Those most similar to apatite are also known as apatites, such as [[lead apatite]] ([[pyromorphite]]) and barium apatite ([[alforsite]]). More chemically dissimilar minerals of the apatite supergroup include [[belovite group|belovite]]s,  [[britholite]]s, [[ellestadite]]s and [[lead apatite|hedyphane]]s.

Apatites have been investigated for their potential use as pigments (copper-doped alkaline earth apatites), as [[phosphor]]s and for absorbing and immobilising toxic heavy metals.

In apatite minerals [[strontium]], [[barium]] and [[lead]] can be substituted for calcium; [[arsenate]] and [[vanadate]] for phosphate; and the final balancing anion can be [[fluoride]] (fluorapatites), [[chloride]] (chlorapatites), [[hydroxide]] (hydroxyapatites) or [[oxide]] (oxyapatites). Synthetic apatites add [[hypomanganate]], [[hypochromate]], [[bromide]] (bromoapatites), [[iodide]] (iodoapatites), [[sulfide]] (sulfoapatites), and [[selenide]] (selenoapatites). Evidence for natural sulfide substitution has been found in lunar rock samples.<ref>{{cite journal|last1=Brounce|first1=Maryjo|last2=Boyce|first2=Jeremy W.|last3=Barnes|first3=Jessica|last4=McCubbin|first4=Francis McCubbin|title=Sulfur in the Apollo Lunar Basalts and Implications for Future Sample-Return Missions|journal=Elements|volume=16|issue=5|date=June 2020|page=361-2|doi=10.2138/gselements.16.5.361 |bibcode=2020Eleme..16..361. }}</ref>

Furthermore, compensating substitution of monovalent and trivalent cations for calcium, of dibasic and tetrabasic anions for phosphate,  and of the balancing anion, can occur to a greater or lesser degree. For example, in biological apatites there is appreciable substitution of sodium for calcium and carbonate for phosphate, in belovite sodium and [[cerium]] or [[lanthanum]] substitute for a pair of divalent metal ions, in germanate-pyromorphite [[germanate]] replaces phosphate and chloride, and in ellestadites silicate and sulphate replace pairs of phosphate anions. Metals forming smaller divalent ions, such as magnesium and iron, cannot substitute extensively for the relatively large calcium ions but may be present in small quantities.<ref>{{cite journal|last1=Kogarko|first1=Lia|title=Chemical Composition and Petrogenetic Implications of Apatite in the Khibiny Apatite-Nepheline Deposits (Kola Peninsula)|journal=Minerals|volume=8|issue=11|date=16 November 2018|page=532|doi=10.3390/min8110532|doi-access=free|bibcode=2018Mine....8..532K }}</ref>

== See also ==
* [[List of minerals]]
* [[Thermal history modelling]]
* [[Hexafluorosilicic acid]]
* [[Hydroxyapatite]] in [[bone]]

==References==
{{Reflist}}
{{Commons category|Apatite}}
{{Wiktionary}}

{{Mohs}}
{{Authority control}}

[[Category:Calcium minerals]]
[[Category:Gemstones]]
[[Category:Radioactive gemstones]]
[[Category:Halide minerals]]
[[Category:Hexagonal minerals]]
[[Category:Minerals in space group 176]]
[[Category:Phosphate minerals]]
[[Category:Piezoelectric materials]]