Mineral description : Pyrrhotite

Massive pyrrhotite from Olden.
Pyrrhotite xx from Outokumpu, Finland.
Pyrrhotite with yellow pyrite from Björkdal gold mine.

Mineral class Sulphides : Pyrrhotite - pentlandite group.
Chemical formula Fe1-xS (x=0-0.2)
Crystal system Hexagonal
Habitus Crystals rare, often hexagonal tabular with horisontal striation. Often as grainy aggregates.
Cleavage None, fracture subconchoidal to uneven.
Hardness 3.5-4.5
Density 4.53-4.77
Color Brass yellow, sometimes with iridescence. Often with a brown tarnish.
Streak Dark gray to black.
Luster Metallic.
Occurance Pyrrhotite forms in magmatic igneous deposits, especially when the rock is of basic or ultrabasic composition. It is also found in highly metamorphic rocks, in hydrothermal veins and sometimes even in pegmatites and sedimentary rocks.
Associates Pyrite, galena, sphalerite and other sulfides.
Notes Magnetic. The magnetism is stronger the less sulphur it contains.
There exists a variant with x=0 which is nonmagnetic and is called troilite. It has been found in meteorites.
Locations A very common mineral in sulphide mines.
  • Bergslagen. Common as massive ore in many mines.
  • Skellefteå district. Common as massive ore in many mines.
  • Liäng limestone quarry, Forsmark, Uppland. As small rounded crystals in calcite.
  • Sala silver mine, Västmanland. Small flat hexagonal crystals in calcite jugs.
  • Nordmarks mine, Värmland. As crystals.
  • Hesselkulla mine, Närke. As crystals.
  • Outokumpu, Finland. As tabular crystals in chromium diopside - calcite scarn.

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Last changed : 1998-03-07