Mineral Species: Pyrophyllite

Chemical Formula: Al2Si4O10(OH)2

Chemical Name: Aluminium Silicate Hydroxide

Mineral Class: Phyllosilicate

Mineral Notes: Pyrophyllite is an early stage metamorphic mineral and found as a constituent of slate, phyllite (not named after pyrophyllite) and some schists. The mineral gets its name from the Greek for fire and leaf as in "fire-leaf" reflecting its luster and because it exfoliates when water ir removed. The structure of pyrophyllite is a stack of silicate-gibbsite-silicate sandwiches. Weak bonding gives rise to Pyrophyllite's softness and perfect cleavage. There are actually two Pyrophyllite species. One is monoclinic and the other triclinic. Usually they would be viewed as two distinct minerals, but their properties are identical and they are often associated and intergrown. Consequently they are normally regarded as one. Finally, Pyrophyllite is isomorphous with Talc.

Description: A specimen consisting of a matrix almost completely formed of Pyrophyllite. Whilst the circular aggregates can be seen on all the surfaces, the best ones are on the top of the specimen. These consist of circular rosettes of bladed crystals, being pale brown in colour and having a very bright silky luster.

Location: Champion Mine, Mono County, California.