Pyrophyllite Locality: Graves Mountain, Lincoln County, Georgia, USA Dimensions: Dimensions: 5" x 4" x 3" Description: Beautiful copper-colored pyrophyllite fro — Photo: John Krygier · Public domain
Pyrophyllite
Also known as: Pencil stone.
A soft aluminium phyllosilicate — talc's aluminium cousin — used for carving stone and refractory ceramics.
Intro adapted from Wikipedia (CC BY-SA).
Pyrophyllite is an IMA-recognized mineral species in the silicate class, with the chemical formula Al₂Si₄O₁₀(OH)₂.
It crystallizes in the triclinic crystal system (space group C2/c). It is a member of the Clay, Pyrophyllite structural group.
Key properties: Mohs hardness 1–1.5; specific gravity 2.65–2.9; typically white or colorless or green or gray or yellow or brown; white streak; Pearly to dull luster; refractive index 1.577; optically biaxial.
IMA symbol Prl, grandfathered status — known before the IMA’s founding, named in 1829.
Somewhat uncommon, found both in hydrothermal veins and in bedded deposits in schistose metamorphic rocks.
It is found associated with Kyanite, andalusite, topaz, mica, quartz.
Its name comes from the Greek for fire and leaf, in allusion to its tendency to exfoliate into fan shapes when heated.
Collections: Collector Favorites, Everyday Minerals.