Pentlandite-pyrrhotite from the Sudbury Impact Structure in Ontario, Canada. (CMNH 12045, Cleveland Museum of Natural History, Cleveland, Ohio, USA)

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 pentlandite ((Ni,Fe)9S8 - nickel iron sulfide) and pyrrhotite (Fe(1-x)S - imperfect iron monosulfide). Sulfide mineralization likely occurred during or very soon after the Sudbury impact event at 1.85 billion years (Paleoproterozoic).

Photo gallery of pentlandite: