Pentlandite in pyrrhotite from the Sudbury Impact Structure in Ontario, Canada. (field of view 8.35 cm across)

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. The massive sulfide rock shown above is from Sudbury.

The Sudbury Complex (Sudbury Basin) in southeastern Canada has intrigued geologists for decades, and not just due to the tremendous economic value of the area’s mineral deposits. Sudbury is one of the largest preserved impact structures on Earth. The impact occurred ~1.85 billion years ago, during the late Paleoproterozoic. The Sudbury Impact Structure is no longer circular or subcircular in shape, however - it's been compessed into a stretched-egg shape from an ancient continental collision event.

This massive sulfide specimen consists of bright brassy-colored patches of pentlandite ((Ni,Fe)9S8 - nickel iron sulfide) in brassy gray-brown pyrrhotite (Fe(1-x)S - imperfect iron monosulfide), plus a network of grayish to black patches of magnetite (Fe3O4 - iron oxide).

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 syn-impact or early post- Impact, 1.85 Ga

Locality: 800 Orebody, South Mine (Copper Cliff South Mine), near Sudbury, southeastern Ontario, southeastern Canada

Photo gallery of pentlandite: