Pyrophyllite Mineral Data

Chemical Formula: Al2(Si4O10)(OH)2

Locality: Tres Cerritos, California, USA; Pyschminsk and Beresovsk, Ural Mountains, Russia.

Name Origin: From the Greek for fie and leaf, in allusion to its tendency to exfoliate into fan shapes when heated.

Pyrophyllite is a phyllosilicate mineral composed of aluminium silicate hydroxide: Al2(Si4O10)(OH)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 fan-like or spherical groups. This variety, when heated before the blowpipe, exfoliates and swells up to many times its original volume, hence the name pyrophyllite, from the Greek pyros (fire) and phyllos (a leaf), given by R. Hermann in 1829. The color of both varieties is white, pale green, greyish or yellowish; they are very soft (hardness of 1 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.

History

Authors: WARDLE & BRINDLEY

Discovery date : 1972

Town of Origin : PYSCHMINSK et BEREZOV, OURAL

Country of Origin: RUSSIE ex-URSS

Chemical properties

Chemical Class : PHYLLOSILICATES

Subclass : Phyllosilicates

Chemical Formula : Al2(Si4O10)(OH)2

Crystallographical properties

Crystalline System: Triclinic

Symmetry Class: 31;32

Network System: Center C  –

a : 5,16

b : 8,96

c : 9,34

Alpha : 91,18

Beta : 100,46

Gamma : 89,64

Z : Formula units per unit cell : 2

Optical properties

Optical and misc. Properties: Translucide –  Opaque

Physical properties

Hardness : from 1,00 to 2,00

Density : 2,70

Color : pearl-white; yellow; brown yellow; pale blue; grey green; grayish green; bluish green

Streak: white

Cleavage: yes