Aluminium silicate hydroxide phyllosilicate mineral
Pyrophyllite
Pearly radial cluster of pyrophyllite from Hillsborough District, Orange County, North Carolina (Size: 11 × 7.3 × 6.6 cm)
General
Category
Silicate minerals
Formula (repeating unit)
Al2Si4O10(OH)2
IMA symbol
Prl[1]
Crystal system
Monoclinic[2] or triclinic[3]
Crystal class
Prismatic (2/m) or pinacoidal (1)
Space group
C2/c or C1
Unit cell
a = 5.16 Å, b = 8.966(3) Å, c = 9.347(6) Å; α = 91.18°, β = 100.46°, γ = 89.64°; Z = 2
Identification
Formula mass
360.31 g/mol
Color
Brown green, brownish yellow, greenish, gray green, gray white
Crystal habit
Compact spherulitic aggregates of needlelike radiating crystals; as
fine grained foliated laminae, granular, massive
Cleavage
[001] Perfect
Tenacity
Flexible inelastic
Mohs scale hardness
1.5–2
Luster
Pearly to dull
Streak
white
Diaphaneity
Translucent to opaque
Specific gravity
2.65 – 2.9
Optical properties
Biaxial (−)
Refractive index
nα=1.534–1.556, nβ=1.586–1.589, nγ=1.596–1.601
Birefringence
δ =0.0450–0.0620
2V angle
53–62
Fusibility
Infusible, exfoliates
References
[2][3][4][5][6][7]
Pyrophyllite is a phyllosilicate mineral composed of aluminium silicate hydroxide: Al2Si4O10(OH)2. It occurs in two forms (habits): crystalline folia and compact masses; distinct crystals are not known.
The folia have a pronounced pearly 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 (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.
^Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., p. 430 ISBN 0-471-80580-7
^Lee, J.H.; Guggenheim, S. (1981). "Single crystal X-ray refinement of pyrophyllite-1Tc". American Mineralogist. 66: 350–357. Retrieved 30 December 2020.
^Gruner, J.W. (1934). "The crystal structures of talc and pyrophyllite". Zeitschrift für Kristallographie. 88 (1–6): 412–419. doi:10.1524/zkri.1934.88.1.412. S2CID 101680970.
Pyrophyllite is a phyllosilicate mineral composed of aluminium silicate hydroxide: Al2Si4O10(OH)2. It occurs in two forms (habits): crystalline folia and...
on 2 July 2013. "Pyrophyllite" (PDF). Division of Resources and Energy, Government of Australia. Retrieved 2 July 2013. "Pyrophyllite - Indian Minerals...
have been collected by miners and rockhounds from 3-billion-year-old pyrophyllite deposits mined by Wonderstone Ltd., near Ottosdal, South Africa. They...
local farmers raise cattle, sheep, pigs, dairy cows and chicken. A major pyrophyllite mine lies near it on the farm Gestoptefontein. This town originated from...
Talc is a trioctahedral layered mineral; its structure is similar to pyrophyllite, but with magnesium in the octahedral sites of the composite layers....
allows the crystals to be pulled apart into very thin elastic sheets. Pyrophyllite, and talc are softer than micas and have a greasy feel, while chlorite...
are mostly red soil in the district. Gold, diamond, quartz, granite, pyrophyllite, road metal, gravel are found in the district. Based on 2011 census,...
montmorillonite-smectite, and illite. Chlorite, vermiculite, talc, and pyrophyllite are sometimes also classified as clay minerals. There are approximately...
Pagodite or agalmatolite is a variety of pyrophyllite used by Chinese artisans for carvings in pagodas and similar objects. Usually soft and sometimes...
quartz to form pyrophyllite (Al2Si4O10(OH)2): Al2Si2O5(OH)4 + SiO2 → Al2Si4O10(OH)2 + H2O As metamorphic grade increases, the pyrophyllite reacts to form...
needles and platelets with other silicates. It is isostructural with the pyrophyllite-talc mineral group. Minnesotaite was first described in 1944 for occurrences...
conditions. Kaolinite and dickite occur at lower temperatures whereas pyrophyllite and andalusite occur under high temperature conditions (T > 300°C). Quartz...
take place, and hydrous aluminosilicate minerals such as muscovite, pyrophyllite, or kaolinite are found instead of kyanite. Bladed crystals of kyanite...
association with quartz, andalusite, rutile, kyanite, corundum, muscovite, pyrophyllite, dumortierite, wagnerite, svanbergite and berlinite in metamorphic terrains;...
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