Pyrrhotite is a magnetic mineral form of iron sulfide (FeS) (but variable), containing more sulfur than pyrite. Pyrrhotite is nonstoichiometric with composition Fe1-xS. Its color is a metallic bronze and forms massive aggregates or hexagonal, flat crystals (monoclinic). It may contain nickel and in such cases is mined as a nickel ore. It occurs in basic igneous rocks, for example in Scandinavia and Ontario. Improved smelting techniques now make it possible to extract the iron. Hardness 3.5–4.5; relative density 4.6.