Nickeline

Nickeline, also known as niccolite, is a mineral species with the chemical formula NiAs, consisting of nickel and arsenic in a 1:1 ratio. It belongs to the nickel arsenide group and crystallizes in the hexagonal system. In hand specimens it typically shows a metallic luster and a lead-gray to steel-gray color, with a dark streak. It commonly forms hexagonal prismatic crystals, but it can also occur as granular or massive aggregates.

Occurrence and geology: Nickeline forms in hydrothermal nickel-bearing ore deposits and in ultramafic rocks. It is often found in association with other nickel minerals such as pentlandite, pyrrhotite, and chalcopyrite. Worldwide occurrences have been reported in several nickel-rich districts, including parts of Norway, Canada, Russia, and Finland. The mineral is of interest primarily as a nickel source in specific ore deposits, rather than as a major standalone ore.

Structure and properties: Nickeline has a relatively high metallic conductivity typical of arsenide minerals. Its hexagonal NiAs-type structure contributes to its characteristic appearance and hardness. On the Mohs scale, its hardness is commonly cited around 4, though exact values can vary with crystal form and impurities.

Etymology and terminology: The name nickeline derives from its nickel content. The spelling niccolite is a traditional synonym used in older literature, and nickeline is an older variant of niccolite that remains in some sources today.

Uses and significance: While nickeline is a nickel-bearing mineral, it is generally a minor ore compared with other nickel minerals in most deposits. It is, however, an important indicator mineral in some nickel-rich hydrothermal systems and contributes to the overall nickel grade when present in ore concentrates.