Formula: Fe7S8 sulphide
Specific gravity: 4.6
Streak: Dark grey
Solubility: Insoluble in water, nitric and sulphuric acid; soluble with decomposition in hydrochloric acid
Plutonic igneous environments
Metamorphic environments (typical)
Pyrrhotite is a primary mineral that may be found as a minor
constituent of some igneous rocks. It is also found in
contact metamorphic deposits, and in the enriched zone of
hypothermal (high temperature) hydrothermal veins.
Pyrrhotite may be found in gabbro and norite (a gabbro where the main mafic mineral is orthopyroxene). It occurs in them as disseminated grains or as large masses associated with pentlandite, chalcopyrite and other sulphides.
At Desolation Prospect, Mount Isa, Australia, trace amounts of pyrrhotite occur as small inclusions in pyrite. Grains of galena are present in the pyrrhotite, which also contains minor cobalt and nickel.
At the Cobar Deposit, Australia, pyrrhotite is associated with early stage gold and with later stage chalcopyrite-cubanite. Where chalcopyrite-cubanite-pyrrhotite overprints early stage gold-bismuthinite, bismuth, gold, scheelite and pyrite apparently are recrystallised.
At Yaogangxian, China, pyrrhotite is often coated with small pyrite crystals.
Common impurities: Ni,Co,Cu