Pentlandite is the principal nickel ore mineral. It is a brassy gold-colored nickel iron sulfide (Ni,Fe)9S8). It's similar in its physical properties to other brassy gold-colored sulfide minerals such as pyrite, pyrrhotite, and chalcopyrite. Pentlandite has a metallic luster, a brassy-bronze color, a light bronzish-brown streak, has a hardness of 3.5 to 4, is not magnetic, has no cleavage, and is moderately heavy for its size. Pentlandite is typically found closely intermingled with pyrrhotite (Fe1-xS), as in the examples shown below. Pentlandite crystals are rare, and it usually occurs in massive to granular form.
Pentlandite can be found with other metallic sulfide minerals, particularly in some mafic and ultramafic intrusive igneous rocks. The Sudbury Impact Structure of Ontario is a world-class locality for pentlandite and other metallic sulfides.
Pentlandite in pyrrhotite (above & below; field of view 3.4 cm across). Bright patches at left & top-center right = pentlandite. Brassy gray-brown areas = pyrrhotite. Black = magnetite.
Geologic Context & Age: Sudbury Impact Structure, late Paleoproterozoic, 1.85 b.y.
Locality: South Mine, near Sudbury, southeastern Ontario, southeastern Canada.
Pentlandite in pyrrhotite (above & below; 8.35 cm across). Bright gold-colored patches = pentlandite. Brassy gray-brown areas = pyrrhotite. Dark grayish to black patches & network = magnetite.
Geologic Context & Age: massive sulfide, 800 Orebody at contact of the Copper Cliff offset dike (quartz diorite) & McKim Formation deltaic metapelites (upper Elliot Group, lower Huronian Supergroup, lower Paleoproterozoic, 2.45 b.y.); sulfide mineralization was early post-Sudbury Impact, late Paleoproterozoic, 1.85 b.y.
Locality: 800 Orebody, South Mine (Copper Cliff South Mine), near Sudbury, southeastern Ontario, southeastern Canada.