Mineral description : Pyrophyllite

Pyrophyllite from a pegmatite in Västerås, Västmanland.
There is some questions about if it's pyrophyllite or some other mineral.

Mineral class Silicates : Phyllosilicates : Serpentinite - talc - Pyrophyllite group
Chemical formula Al2(OH)2(Si4O10)
Crystal system Monoclinic.
Habitus As radiating groups of soft lamellaes. Often as massive aggregates.
Cleavage Good. (Massive variants none.)
Hardness 1-2 (Could contain other minerals, making it harder.)
Density 2.66-2.90
Color Yellowish white to yellowish brown, light green.
Streak White.
Luster Pearly, massive forms greasy.
Description Pyrophyllite is used as talc sometimes, but since talc is better and cheaper it's use is limited.
The main usage of pyrophyllite is as a carrier for insectoides and is used as a filler in these products.
Occurance Created through hydrothermal transformation of aluminum rich rocks. Light green masses of serpentinite looking minerals are often pyrophyllite.
Andalusite in quartz is often coated by soft yellow pyrophyllite.
Associates Sillimanite, andalusite.
Notes The lamellaes are bendable but are not flexible.
Greasy feeling.
The name comes from the Greek words pyro (fire) and phyllos (leaf), since it expands when heated and falls apart in thin leafs.
It is very hard to discern pyrophyllite from talc without chemical methods. One method is to test for aluminum with the aid of a cobalt nitrate solution. A few drops are applied at the sample and then heating the sample until it glows. If the sample changes to a blue color it is pyrophyllite, if it turns violet it is talc.
A good reference is "Mineral och Bergarter" by Erich Spicar, page 81.
Locations A not so rare mineral, often mistaken as talc.
  • Västanågruvan, Skåne. As nice yellowish white leafy radial aggregates.
  • Horrsjöberg, Värmland. As weakly greenish blue flakes with kyanite. Created by hydrothermal transformation of acidic eruptives.
  • Norrö, in the archipelago of Stockholm.
  • Bliaberget, Ransäter, Värmland.
  • Kolsva, Västmanland. As transformation of sillimanite.
  • Västerås, Västmanland. As green masses in a pegmatite with quartz and feldspar.
  • Viitaniemi, Finland. At the side, and together with a yellow muscovite are yellow pyrophyllite.
  • China. Pure pyromorphite are called agalmatolite. It is used for artworks and is sold as soapstone, which is wrong.

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Last changed : 1998-04-16