pentlandiit

Pentlandite (Finnish: pentlandiit) is a nickel-iron sulfide mineral with the approximate formula (Fe,Ni)9S8. It forms a solid solution between iron-rich and nickel-rich compositions and is the most important primary ore mineral of nickel.

Geology and occurrence: Pentlandite occurs in ultramafic and mafic rocks, especially in igneous sulfide deposits within peridotites such as dunites and harzburgites, and in layered intrusions. It is commonly associated with pyrrhotite, pyrite, chalcopyrite and magnetite, and appears as disseminated grains or large masses within sulfide ore bodies. It is a major source of nickel in many magmatic sulfide systems.

Physical properties: Pentlandite has a metallic luster and a bronze-yellow to brownish color in hand specimen. It crystallizes in the isometric (cubic) system and typically occurs as grains ranging from microscopic to centimeter scale. Hardness is about 4 on the Mohs scale, and the specific gravity is roughly 4.8–5.0. It shows little to no cleavage and forms in finely granular to massive textures in ore bodies.

Occurrence and significance: Pentlandite is globally important as the principal nickel ore. Nickel is extracted commercially from pentlandite-rich sulfide deposits, often together with other sulfide minerals such as pyrrhotite and chalcopyrite. The mineral helps define nickel-rich ultramafic ore systems and is a key indicator in exploration for Ni-Cu-PGE sulfide deposits.

Etymology: The name pentlandite derives from the Pentland Hills near Edinburgh, Scotland, where the mineral was first described.