Editing Pyrophyllite (section)

{{short description|Aluminium silicate hydroxide phyllosilicate mineral}}
{{Infobox mineral
| name        = Pyrophyllite
| category    = [[Silicate minerals]]
| boxwidth    = 
| boxbgcolor  =#dfce9d 
| image       = Pyrophyllite-118706.jpg
| imagesize   = 260px
| 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]]<ref name=Mindat/> or [[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 [[Silicate minerals|phyllosilicate]] [[mineral]] composed of [[aluminium]] [[silicate]] [[hydroxide]]: Al<sub>2</sub>Si<sub>4</sub>O<sub>10</sub>(OH)<sub>2</sub>. It occurs in two forms ([[Crystal habit|habit]]s): crystalline folia and compact masses; distinct [[crystal]]s are not known.

The folia have a pronounced pearly [[Lustre (mineralogy)|luster]], 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 ([[Mohs hardness|hardness]] of 1.0 to 1.5) and are greasy to the touch. The [[specific gravity]] is 2.65–2.85. The two varieties are thus very similar to [[talc]].