What is Nickeline?
Nickeline is a copper-red nickel arsenide from hydrothermal nickel deposits, important as an ore mineral and a striking metallic collector specimen.
Mineralogy and crystal structure
Reference formula: NiAs. Nickeline has a hexagonal NiAs-type structure and commonly alters to annabergite and other green nickel minerals. Its copper-red colour and heavy metallic feel are characteristic but arsenic requires caution. Nickeline is classified with sulfides and has a hexagonal crystal system. Typical hardness is 5–5.5 on the Mohs scale and specific gravity is approximately 7.6–7.8.
Colour, lustre and habit
Typical colours include copper-red, bronze, grey, black. The usual massive, granular, tabular habit and metallic lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Nickeline forms in or is associated with hydrothermal nickel arsenide veins, ultramafic ore systems and contact-metamorphic deposits. Important documented localities include Germany, Canada, Morocco, Norway, Chile and the United States.
Copper-red metal from a nickel vein
Nickeline is unusually colourful for a metallic sulfide. Its warm red surface, high density and alteration to green nickel minerals make a small specimen a compact ore-geology lesson.
Collecting and care
Arsenic- and nickel-bearing: keep enclosed, avoid dust, cutting and acids, and wash hands after handling.
