A mineral having composition (Fe,Ni)₉S₈. Pentlandite is the major ore of nickel. It crystallizes in the isometric system, but crystals are rare. It is usually massive, showing a well-defined octahedral parting. The hardness is 3.5–4 (Mohs scale) and the specific gravity varies from 4.6 to 5.0, depending on the ratio of iron to nickel; greater amounts of iron cause an increase in the specific gravity. The luster is metallic and the color yellowish bronze. Pentlandite is usually associated with pyrrhotite, which it closely resembles in appearance, but the two can be distinguished by the octahedral parting and lack of magnetism of pentlandite. It is found at many localities in small amounts, but its chief occurrence is at Sudbury, Ontario, where it is mined on a large scale as a nickel ore.