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PYROPHYLLITE , a See also: mineral See also: species belonging to the See also: clay See also: family, and composed of hydrous aluminium silicate See also: HAl (SiO3)2
.
It occurs in two more or less distinct varieties, namely, as crystalline folia and as compact masses; distinct crystals are not known
.
The folia have a pronounced pearly lustre, owing to the presence of a perfect cleavage parallel to their surfaces: they are flexible but not elastic, and are usually arranged radially in See also: fan-like or spherical See also: groups
.
This variety, when heated before the See also: blowpipe, exfoliates and swells up to many times its See also: original See also: volume, hence the name pyrophyllite, from the See also: Greek 76p (fire) and quahov (a leaf), given by R
.
Hermann in 1829
.
The colour of both varieties is See also: white, pale
See also: green, greyish or yellowish ; they are very soft (H
.
= 1–2) and are greasy to the touch
.
The specific gravity is 2.8–2.9
.
The two varieties are thus very similar respectively to See also: talc (q.v.) and its compact variety steatite, which is, however, a hydrous magnesium
H See also: C2H
//',,,.// O
\C.C6H3(OH)2 CO/`OH
See also: C6H4
silicate
.
The compact variety of pyrophyllite is used for slate pencils and tailors' See also: chalk (" French chalk "), and is carved by the See also: Chinese into small images and ornaments of various kinds
.
Other soft compact minerals (steatite and pinite) used for these Chinese carvings are included with pyrophyllite under the terms agalmatolite and pagodite
.
Pyrophyllite occurs in schistose rocks, often associated with See also: cyanite, of which it is an alteration product
.
Pale green foliated masses, very like talc in appearance, are found at Beresovsk nearSee also: Ekaterinburg in the Urals, and at See also: Zermatt in See also: Switzerland
.
The most extensive deposits are in the Deep See also: river region of See also: North Carolina, where the compact variety is See also: mined, and in See also: South Carolina and See also: Georgia
.
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