Polydymite, Ni2+Ni23+S4, is a supergene thiospinel associated with the weathering of primary pentlandite nickel sulfide.
Polydymite crystallises in the isometric system, with a hardness of 4.5 to 5.5 and a specific gravity of about 4, is dark violet gray to copper-red, often with verdigris and patina from associated copper and arsenic sulfides, and is typically in amorphous to massive infill of lower saprolite.
Polydymite is the nickel equivalent of violarite and in many cases these two minerals are formed together, potentially in solid solution.
Common contaminants of polydymite are cobalt and iron. Polydymite forms a series with linnaeite