# Pyrophyllite

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{{Short description|Phyllosilicate mineral in the pyrophyllite-talc group}}
{{Infobox mineral
| name        = Pyrophyllite
| category = [Phyllosilicate](/source/Phyllosilicate) minerals
| group = Pyrophyllite-[Talc](/source/Talc) group
| boxwidth    = 
| boxbgcolor  =#dfce9d 
| image       = Pyrophyllite-118706.jpg
| caption     = Pearly radial cluster of pyrophyllite from Hillsborough District, Orange County, North Carolina (Size: 11 × 7.3 × 6.6 cm)
| formula     = Al<sub>2</sub>Si<sub>4</sub>O<sub>10</sub>(OH)<sub>2</sub>
| IMAsymbol   = Prl<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   = 360.31 g/mol
| system      = [Monoclinic](/source/Monoclinic)<ref name=Mindat/> or [triclinic](/source/triclinic)<ref name=Webmin/>
| class       = Prismatic (2/m) <br/>or pinacoidal ({{overline|1}})
| symmetry    = ''C2/c'' or ''C{{overline|1}}''
| unit cell   = a = 5.16&nbsp;Å, <br/>b = 8.966(3)&nbsp;Å, <br/>c = 9.347(6)&nbsp;Å; α = 91.18°, <br/>β = 100.46°, γ = 89.64°; Z&nbsp;=&nbsp;2
| color       = Brown green, brownish yellow, greenish, gray green, gray white
| habit       = Compact spherulitic aggregates of needlelike radiating crystals; as
fine grained foliated laminae, granular, massive
| cleavage    = [001] Perfect 
| tenacity    = Flexible inelastic
| mohs        = 1.5–2
| luster      = Pearly to dull 
| refractive  = n<sub>α</sub>=1.534–1.556, n<sub>β</sub>=1.586–1.589, n<sub>γ</sub>=1.596–1.601
| opticalprop = Biaxial (−) 
| 2V          = 53–62
| birefringence = δ =0.0450–0.0620
| pleochroism = 
| streak      = white
| gravity     = 2.65 – 2.9
| melt        = 
| fusibility  = Infusible, exfoliates 
| diagnostic  = 
| solubility  = 
| diaphaneity = Translucent to opaque
| other       = 
| references  =<ref name=Mindat>[http://www.mindat.org/min-3323.html Mindat]</ref><ref name=Webmin>http://webmineral.com/data/Pyrophyllite.shtml Webmineral</ref><ref name=Handbook>[http://rruff.geo.arizona.edu/doclib/hom/pyrophyllite.pdf Handbook of Mineralogy]</ref><ref name=Klein>Hurlbut, Cornelius S.; Klein, Cornelis, 1985, ''Manual of Mineralogy,'' 20th ed., p. 430 {{ISBN|0-471-80580-7}}</ref><ref>{{cite journal |last1=Lee |first1=J.H. |last2=Guggenheim |first2=S. |journal=American Mineralogist |volume=66 |year=1981 |pages=350–357 |title=Single crystal X-ray refinement of pyrophyllite-1Tc |url=https://pubs.geoscienceworld.org/msa/ammin/article-abstract/66/3-4/350/41261/Single-crystal-X-ray-refinement-of-pyrophyllite?redirectedFrom=fulltext |access-date=30 December 2020}}</ref><ref>{{cite journal |last1=Gruner |first1=J.W. |journal=Zeitschrift für Kristallographie |volume=88 |year=1934 |pages=412–419 |title=The crystal structures of talc and pyrophyllite|issue=1–6 |doi=10.1524/zkri.1934.88.1.412 |s2cid=101680970 }}</ref>
}}

'''Pyrophyllite''' is a [phyllosilicate](/source/Silicate_minerals) [mineral](/source/mineral) composed of [aluminium](/source/aluminium) [silicate](/source/silicate) [hydroxide](/source/hydroxide): Al<sub>2</sub>Si<sub>4</sub>O<sub>10</sub>(OH)<sub>2</sub>. It occurs in two forms ([habit](/source/Crystal_habit)s): crystalline folia and compact masses; distinct [crystal](/source/crystal)s are not known.

The folia have a pronounced pearly [luster](/source/Lustre_(mineralogy)), owing to the presence of a perfect cleavage parallel to their surfaces: they are flexible but not elastic, and are usually arranged radially in fan-like or spherical groups. This variety, when heated, exfoliates and swells up to many times its original volume. The color of both varieties is white, pale green, greyish or yellowish; they are very soft ([hardness](/source/Mohs_hardness) of 1.0 to 1.5) and are greasy to the touch. The [specific gravity](/source/specific_gravity) is 2.65–2.85. The two varieties are thus very similar to [talc](/source/talc).

==Occurrence==
Pyrophyllite occurs in [phyllite](/source/phyllite) and [schist](/source/schist)ose rocks, often associated with [kyanite](/source/kyanite), of which it is an alteration product. It also occurs as [hydrothermal](/source/hydrothermal) deposits. Typical associated minerals include: kyanite, [andalusite](/source/andalusite), [topaz](/source/topaz), [mica](/source/mica) and [quartz](/source/quartz).<ref name=Handbook/>

Deposits containing well-crystallized material are found in:<ref name=Handbook/>
* [Manuels](/source/Manuels%2C_Newfoundland_and_Labrador), [Newfoundland and Labrador](/source/Newfoundland_and_Labrador), Canada, talc-like bright white appearance, high grade, no impurities; 21 million ton deposit. 
*Russia – pale green foliated masses, very like talc in appearance, are found at [Beresovsk](/source/Beresovsk) near [Yekaterinburg](/source/Yekaterinburg) in the [Ural](/source/Ural_Mountains)s.
* St. Niklas, [Zermatt](/source/Zermatt), [Valais](/source/Valais), [Switzerland](/source/Switzerland)
* Vaastana, [Kristianstad](/source/Kristianstad), [Sweden](/source/Sweden)
* Near Ottrje, [Ardennes Mountains](/source/Ardennes_Mountains), [Belgium](/source/Belgium)
* [Ibitiara](/source/Ibitiara), [Bahia](/source/Bahia), [Brazil](/source/Brazil)
* [Nagano Prefecture](/source/Nagano_Prefecture), [Japan](/source/Japan)
* Near [Ogilby](/source/Ogilby%2C_California), [Imperial County](/source/Imperial_County%2C_California) at Tres Cerritos, [Mariposa County](/source/Mariposa_County%2C_California), and the Champion mine, White Mountains, [Mono County, California](/source/Mono_County%2C_California), US
* Near [Quartzsite](/source/Quartzsite), [La Paz County, Arizona](/source/La_Paz_County%2C_Arizona), US
* Large deposits at the [Deep River](/source/Deep_River_(North_Carolina)) region of [North Carolina](/source/North_Carolina), USA
*Graves Mountain, [Lincoln County, Georgia](/source/Lincoln_County%2C_Georgia), US

In South Africa, major deposits of pyrophyllite occur within the [Ottosdal](/source/Ottosdal) region, where it is mined for the production of a variety of manufactured goods, and blocks are quarried and marketed as "Wonderstone" for the carving of sculptures.<ref name="NelOthers1937">Nel, LT., H. Jacobs, J.T. Allen and G.R. Bozzoli 1937. ''Wonderstone''. Geological Survey of South Africa Bulletin no. 8.</ref>

==Uses==
The compact variety of pyrophyllite is used for slate pencils and tailors' chalk ([French chalk](/source/French_chalk)), and is carved by the Chinese into small images and ornaments of various kinds. Other soft compact minerals ([steatite](/source/steatite) and [pinite](/source/pinite)) used for these Chinese carvings are included with pyrophyllite under the terms [agalmatolite](/source/agalmatolite) and [pagodite](/source/pagodite).{{Citation needed|date=August 2010}}

Pyrophyllite is easily machineable and has excellent thermal stability, so it is added to clay to reduce thermal expansion when firing, but it has many other industrial uses when combined with other compounds, such as in insecticide and for making bricks. Pyrophyllite is also widely used in [high-pressure](/source/Pressure_experiment) experiments, both as a [gasket](/source/diamond_anvil_cell) material and as a pressure-transmitting medium.<ref>{{cite journal| title = Effect of precompression on pressure-transmitting efficiency of pyrophyllite gaskets| author= L. Fang| doi = 10.1080/08957950701553796| journal = Journal High Pressure Research| volume =27| year = 2007 | issue= 3| page = 367|bibcode = 2007HPR....27..367F | s2cid= 97317483|display-authors=etal}}</ref>

==See also==
* {{annotated link|Talc}}

==References==
{{Reflist}}

==External links==
*[https://web.archive.org/web/20050513215604/http://mineral.galleries.com/minerals/silicate/pyrophyl/pyrophyl.htm Mineral galleries]
*[https://minerals.usgs.gov/minerals/pubs/commodity/talc/ USGS]

{{Phyllosilicates}}

{{EB1911|wstitle=Pyrophyllite|volume=22|pages=695–696}}

Category:Aluminium minerals
Category:Triclinic minerals
Category:Monoclinic minerals
Category:Minerals in space group 2
Category:Minerals in space group 15
Category:Luminescent minerals
Category:Pyrophyllite-Talc group

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Adapted from the Wikipedia article [Pyrophyllite](https://en.wikipedia.org/wiki/Pyrophyllite) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Pyrophyllite?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.