For this reason, the best way to discern pentlandite is by its paler color, lack of magnetism, and light brownish bronze streak.

Pentlandite usually develops as granular inclusions within other sulfide minerals (mainly pyrrhotite), often taking the shape of thin veins or "flames".

Their chemical formula can be written as XY8(S, Se)8 in which X is usually replaced by silver, manganese, cadmium, and lead, while copper takes the place of Y.

[20] In sulfide undersaturated melts, nickel substitutes for other transition metals within ferromagnesian minerals, the most common being olivine, as well as nickeliferous varieties of amphibole, biotite, pyroxene and spinel.

This phase is called monosulfide solid solution (MSS), and is unstable at low temperatures decomposing to mixtures of pentlandite and pyrrhotite, and (rarely) pyrite.

Metamorphism at a grade equal to, or higher than, greenschist facies will cause solid massive sulfides to deform in a ductile fashion and to travel some distance into the country rock and along structures.

[23] Upon cessation of metamorphism, the sulfides may inherit a foliated or sheared texture, and typically develop bright, equigranular to globular aggregates of porphyroblastic pentlandite crystals known colloquially as "fish scales".

Metamorphism may also be associated with metasomatism, and it is particularly common for arsenic to react with pre-existing sulfides, producing nickeline, gersdorffite and other Ni–Co arsenides.

[25] Pentlandite is found within the lower margins of mineralized layered intrusions, the best examples being the Bushveld igneous complex, South Africa, the Voisey's Bay troctolite intrusive complex in Canada, the Duluth gabbro, in North America, and various other localities throughout the world.

Pentlandite, but primarily chalcopyrite and PGEs, are also obtained from the supergiant Norilsk nickel deposit, in trans-Siberian Russia.