Pentlandite is an iron-nickel sulfide, (Fe,Ni)9S8. Pentlandite usually has a Ni:Fe ratio of close to 1:1. It also contains minor cobalt. Pentlandite forms isometric crystals, but is normally found in massive granular aggregates. It is brittle with a hardness of 3.5 - 4 and specific gravity of 4.6 - 5.0 and is non-magnetic. It has a yellowish bronze color
Pentlandite is the most common terrestrial nickel sulfide mineral formed from immiscible sulfide-silicate melts under normal mantle and crustal conditions. Nickel, being a chalcophile element, prefers to inhabit a sulfide phase versus a silicate or oxide phase within most terrestrial lithochemical systems (a few exceptions exist in unusual compositions). This behaviour is seen only when the particular rock is molten and sulfur saturated.