Nickeline or niccolite is the mineral form of nickel arsenide. The naturally occurring mineral contains roughly 43.9% nickel and 56.1% arsenic by mass, but composition of the mineral may vary slightly. This German equivalent of "copper-nickel" was used as early as 1694 (other old German synonyms are Rotnickelkies and Arsennickel).
In 1751, Baron Axel Fredrik Cronstedt was attempting to extract copper from kupfernickel mineral, and obtained instead a white metal which he named "nickel", after the sprite. In modern German, Kupfernickel and Kupfer-Nickel designates the alloy Cupronickel.
The names subsequently given to the ore, nickeline from F. S. Beudant, 1832, and niccolite, from J. D. Dana, 1868, refer to the presence of nickel; in Latin, niccolum.
In 1971, the International Mineralogical Association recommended use of the name nickeline rather than niccolite.
Occurrence
Nickeline is formed by hydrothermal modification of ultramafic rocks and associated ore deposits, and may be formed by replacement of nickel-copper bearing sulfides (replacing pentlandite, and in association with copper arsenic sulfides), or via metasomatism of sulfide-free ultramafic rocks, where metasomatic fluids introduce sulfur, carbonate, and arsenic. This typically results in mineral assemblages including millerite, heazelwoodite and metamorphic pentlandite-pyrite via sulfidation and associated arsenopyrite-nickeline-breithauptite.
Associated minerals include: arsenopyrite, barite, silver, cobaltite, pyrrhotite, pentlandite, chalcopyrite, breithauptite and maucherite. Nickeline alters to annabergite (a coating of green nickel arsenate) on exposure to moist air.
Most of these minerals can be found in the areas surrounding Sudbury and Cobalt, Ontario. Other localities include the eastern flank of the Widgiemooltha Dome, Western Australia, from altered pentlndite-pyrite-pyrrhotite assemblages within the Mariners, Redross and Miitel nickel mines where nickeline is produced by regional Au-As-Ag-bearing alteration and carbonate metasomatism. Other occurrences include within similarly modified nickel mines of the Kambalda area.
Crystal structure
The unit cell of nickeline is used as the prototype of a group of crystalline solids with similar crystal structures. The structure consists of two interpenetrating sublattices: a primitive hexagonal nickel sublattice and a hexagonal close-packed arsenic sublattice. Each nickel atom is octahedrally coordinated to six arsenic atoms, while each arsenic atom is trigonal prismatically coordinated to six nickel atoms. Compounds adopting the NiAs structure are generally the chalcogenides, arsenides, antimonides and bismuthides of transition metals.
thumb|The unit cell of nickeline
The following are the members of the nickeline group: