Editing Pyrochlore

{{short description|Niobium mineral of A2B2O7 general formula}}
{{Infobox mineral
| name        = Pyrochlore
| category    = [[Oxide mineral]]
| boxwidth    = 
| boxbgcolor  = 
| image       = Pyrochlore-180063.jpg
| caption     = Pyrochlore from Russia
| formula     = {{chem2|(Na,Ca)2Nb2O6(OH,F)}}
| IMAsymbol   = Pcl<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      = 4.DH.15
| dana        = 08.02.01.01 <br/>Pyrochlore group
| system      = [[Cubic (crystal system)|Isometric]] 
| class       = Hexoctahedral (m{{overline|3}}m) <br/>[[H-M symbol]]: (4/m {{overline|3}} 2/m)
| symmetry    = ''F''d{{overline|3}}m (No. 227)
| unit cell   = ''a''&nbsp;=&nbsp;10.41(6)&nbsp;Å, ''Z''&nbsp;=&nbsp;8
| color       = Black to brown, chocolate-brown, reddish brown, amber-orange, red-orange
| habit       = Typically octahedra, disseminated granular, massive
| twinning    = 111 rare
| cleavage    = 111 indistinct, may be a parting.
| fracture    = Subconchoidal to uneven, splintery
| tenacity    = Brittle
| mohs        = 5.0–5.5
| luster      = Vitreous to resinous
| polish      = 
| refractive  = ''n''&nbsp;=&nbsp;1.9–2.2
| opticalprop = Isotropic, weak anomalous anisotropism
| birefringence = 
| pleochroism = 
| streak      = White
| gravity     = 4.45 to 4.90
| melt        = 
| fusibility  = 
| diagnostic  = 
| solubility  = 
| diaphaneity = Subtranslucent to opaque
| other       = [[Image:Radioactive.svg|25px]] [[Radioactive]], often [[metamict]]
| references  = <ref>{{Cite web|url=https://www.mineralienatlas.de/lexikon/index.php/MineralData?lang=de&mineral=Pyrochlor|title=Pyrochlor|website=www.mineralienatlas.de}}</ref><ref name="Handbook">{{Cite web |title = pyrochlore at RRuff database |work = rruff.info |access-date = 2015-02-03 |url = http://rruff.info/doclib/hom/pyrochlore.pdf}}</ref><ref name="Mindat">{{Cite web |title = Pyrochlore Group: Pyrochlore Group mineral information and data. |work = mindat.org |access-date = 2015-02-03 |url = http://www.mindat.org/min-3316.html}}</ref><ref name="webmin">{{Cite web |title = Pyrochlore Mineral Data |last = Barthelmy |first = Dave |work = webmineral.com |access-date = 2015-02-03 |url = http://webmineral.com/data/Pyrochlore.shtml#.VNGZoUejO-0}}</ref>
}}
'''Pyrochlore''' ({{chem2|[[sodium|Na]],[[calcium|Ca]])2[[niobium|Nb]]2[[oxygen|O]]6([[hydroxide|OH]],[[fluorine|F]]}}) is a mineral group of the [[niobium]] end member of the pyrochlore supergroup. Pyrochlore is also a term for the crystal structure [[Cubic crystal system#Crystal classes|''F''d{{overline|3}}m]]. The name is from the [[Ancient Greek language|Greek]] {{lang|grc|πῦρ}}, ''fire'', and {{lang|grc|χλωρός}}, ''green'' because it typically turns green on ignition in classic blowpipe analysis.<ref name="Mindat" />

== Mineral ==
The general formula, {{chem2|A2B2O7}} (where A and B are metals), represent a family of phases isostructural to the mineral pyrochlore. Pyrochlores are an important class of materials in diverse technological applications such as luminescence, ionic conductivity, nuclear waste immobilization, high-temperature thermal barrier coatings, automobile [[exhaust gas]] control, catalysts, solid oxide fuel cell, ionic/electrical conductors etc.

The mineral is associated with the [[Metasomatism|metasomatic]] end stages of magmatic intrusions. Pyrochlore crystals are usually well-formed (euhedral), occurring usually as [[octahedron|octahedra]] of a yellowish or brownish color and [[resin]]ous luster. It is commonly [[metamict]] due to radiation damage from included radioactive elements.

Pyrochlore occurs in [[pegmatite]]s associated with [[nepheline syenite]]s and other alkalic rocks. It is also found in [[granite]] pegmatites and [[greisen]]s. It is characteristically found in [[carbonatite]]s. Associated minerals include [[zircon]], [[aegirine]], [[apatite]], [[perovskite]] and [[columbite]].<ref name="Handbook" />

=== History ===
It was first described in 1826 for an occurrence in Stavern (Fredriksvärn), [[Larvik]], Vestfold, Norway.<ref name="Mindat" />

=== Niobium mining ===
The three largest producers of niobium ore are mining pyrochlore deposits. The largest deposit in [[Brazil]] is the CBMM mine located south of [[Araxá]], Minas Gerais, followed by the deposit of the Catalão mine east of [[Catalão]], Goiás. The third largest deposit of niobium ore is Niobec mine west of [[Saint-Honoré, Quebec|Saint-Honoré]] near [[Chicoutimi]], Quebec.<ref name="tesla">{{cite web |last1=Kouptsidis |first1=J. |last2=Peters |first2=F. |last3=Proch |first3=D. |last4=Singer |first4=W. |title=Niob für TESLA |url=http://tesla.desy.de/new_pages/TESLA_Reports/2001/pdf_files/tesla2001-27.pdf |url-status=dead |archive-url=https://web.archive.org/web/20081217100548/http://tesla.desy.de/new_pages/TESLA_Reports/2001/pdf_files/tesla2001-27.pdf |archive-date=2008-12-17 |access-date=2008-09-02}}</ref>

Pyrochlore ore typically contains greater than 0.05% of naturally occurring radioactive [[uranium]] and [[thorium]].<ref>{{Cite journal |last1=Dias da Cunha |first1=K. |last2=Santos |first2=M. |last3=Zouain |first3=F. |last4=Carneiro |first4=L. |last5=Pitassi |first5=G. |last6=Lima |first6=C. |last7=Barros Leite |first7=C. V. |last8=Dália |first8=K. C. P. |date=May 8, 2009 |title=Dissolution Factors of Ta, Th, and U Oxides Present in Pyrochlore |journal=Water, Air, & Soil Pollution |volume=205 |issue=1–4 |pages=251–257 |doi=10.1007/s11270-009-0071-3 |issn=0049-6979 |s2cid=93478456}}</ref>

[[Lueshe]] in [[North Kivu]], Democratic Republic of Congo, has substantial deposits of pyrochlore.<ref>{{Cite web |title=Blood Minerals in the Kivu Provinces |url=https://www.globalpolicy.org/component/content/article/181/33658.html |website=www.globalpolicy.org}}</ref>

==Crystal structure==
The more general crystal structure describes materials of the type A<sub>2</sub>B<sub>2</sub>O<sub>6</sub> and A<sub>2</sub>B<sub>2</sub>O<sub>7</sub> where the A and B species are generally rare-earth or transition metal species; e.g. Y<sub>2</sub>Ti<sub>2</sub>O<sub>7</sub>.The pyrochlore structure is a super structure derivative of the simple [[fluorite structure]] (AO<sub>2</sub> = A<sub>4</sub>O<sub>8</sub>), where the A and B cations are ordered along the {{angbr|110}} direction. The additional anion vacancy resides in the tetrahedral interstice between adjacent B-site cations. These systems are particularly susceptible to [[geometrical frustration]] and novel magnetic effects.

The pyrochlore structure shows varied physical properties spanning electronic [[Insulator (electricity)|insulators]] (e.g. La<sub>2</sub>Zr<sub>2</sub>O<sub>7</sub>), [[Ionic conductivity (solid state)|ionic conductors]] (Gd<sub>1.9</sub>Ca<sub>0.1</sub>Ti<sub>2</sub>O<sub>6.9</sub>), [[Electrical conductivity#In metals|metallic conductors]] (Bi<sub>2</sub>Ru<sub>2</sub>O<sub>7−''y''</sub>), mixed ionic and electronic conductors, [[spin ice]] systems (Dy<sub>2</sub>Ti<sub>2</sub>O<sub>7</sub>), [[spin glass]] systems (Y<sub>2</sub>Mo<sub>2</sub>O<sub>7</sub>), haldane chain systems (Tl<sub>2</sub>Ru<sub>2</sub>O<sub>7</sub>) and [[Superconductivity|superconducting materials]] (Cd<sub>2</sub>Re<sub>2</sub>O<sub>7</sub>).<ref>{{Cite journal |last1=Subramanian |first1=M. A. |last2=Aravamudan |first2=G. |last3=Subba Rao |first3=G. V. |date=1983-01-01 |title=Oxide pyrochlores — A review |journal=Progress in Solid State Chemistry |volume=15 |issue=2 |pages=55–143 |doi=10.1016/0079-6786(83)90001-8}}</ref> More disordered structures, such as the bismuth pyrochlores,<ref>Arenas, D. J., et al. "Raman study of phonon modes in bismuth pyrochlores." Physical Review B 82.21 (2010): 214302. | https://doi.org/10.1103/PhysRevB.82.214302</ref> have also been investigated due to interesting high-frequency dielectric properties.<ref>Cann, David P., [[Clive Randall|Clive A. Randall]], and Thomas R. Shrout. "Investigation of the dielectric properties of bismuth pyrochlores." Solid state communications 100.7 (1996): 529–534. | https://doi.org/10.1016/0038-1098(96)00012-9</ref>

The crystal structure has been investigated for use in solid electrolytes for [[Lithium-ion battery|lithium iron batteries]]. It is alleged to provide high conductivity while inhibiting dendrite growth.<ref>{{Cite web |last=Ettlin |first=Anna |date=2023-11-07 |title=What Is The Battery Of The Future Made Of? |url=https://cleantechnica.com/2023/11/07/what-is-the-battery-of-the-future-made-of/ |access-date=2023-11-15 |website=CleanTechnica |language=en-US}}</ref>

==See also==
{{stack|{{Commons category|Pyrochlore}} }}
* [[List of minerals]]

==References==
{{Reflist}}

*{{cite journal|last2= Andrade|first2= M. B. |date=2022 |title=Prospection of pyrochlore and microlite mineral groups through Raman spectroscopy coupled with artificial neural networks |journal=Journal of Raman Spectroscopy |doi=10.1002/jrs.6433|last1=Queiroz|first1= A. A. A. E.|volume= 53 |issue= 11 |pages= 1924–1930 |bibcode= 2022JRSp...53.1924E |s2cid= 251463725 }}

[[Category:Sodium minerals]]
[[Category:Calcium minerals]]
[[Category:Niobium minerals]]
[[Category:Radioactive gemstones]]
[[Category:Oxide minerals]]
[[Category:Cubic minerals]]
[[Category:Minerals in space group 227]]
[[Category:Minerals described in 1826]]