Niccolite or nickeline is a mineral consisting of nickel arsenide, NiAs, containing 43.9% nickel and 56.1% arsenic.
Small quantities of sulfur, iron and cobalt are usually present, and sometimes the arsenic is largely replaced by antimony. Forms an isomorphous series with breithauptite (nickel antimonide).
The names niccolite (J. D. Dana, 1868) and nickeline (F. S. Beudant, 1832) refer to the presence of nickel (Lat. niccolum). Owing to its copper-red color the mineral is commonly called "copper-nickel," the German equivalent of which, Kupfernickel, was used as early as 1694.
Associated minerals include: arsenopyrite, barite, silver, cobaltite, pyrrhotite, pentlandite, chalcopyrite, breithauptite and maucherite. Niccolite alters to annabergite (a coating of green nickel arsenate) on exposure to moist air.
Niccolite is formed by hydrothermal modification of ultramafic rocks and associated ore deposits, and may be formed by replacement of nickel-copper bearing sulphides (replacing pentlandite, and in association with copper arsenic sulfides), or via metasomatism of sulphide-free ultramafic rocks, where metasomatic fluids introduce sulphur, carbonate, and arsenic. This typically results in mineral assemblaged including millerite, heazelwoodite and metamorphic pentlandite-pyrite via sulfidation and associated arsenopyrite-niccolite-breithauptite.
Most of these minerals can be found in the areas surrounding Greater Sudbury, Ontario 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 niccolite is produced by regional Au-As-Ag-bearing alteration and carbonate metasomatism. Other occurrences include within similarly modified nickel mines of the Kambalda area.
The unit cell of niccolite is used the prototype of a class of solids with similar crystal structures. Compounds adopting the NiAs structure are generally the chalcogenides, arsenides, antimonides and bismuthides of transition metals. Members of this group include cobalt(II) sulfide and iron(II) sulfide.
Breithauptite: nickel antimonide, NiSb
Freboldite: cobalt selenide, CoSe
Imgreite: nickel telluride, NiTe
Langistite: cobalt nickel arsenide, (Co,Ni)As
Niccolite: nickel arsenide, NiAs
Pyrrhotite: iron sulfide Fe1-xS
Sederholmite: nickel selenide, NiSe
Stumpflite: platinum antimonide bismuthinide, Pt(Sb,Bi)
Sudburyite: palladium nickel antimonide, (Pd,Ni)Sb
Niccolite is rarely used as a source of nickel due to the presence of arsenic, which is deleterious to most smelting and milling techniques. When nickel sulphide ore deposits have been altered to produce niccolite, often the presence of arsenic renders the ore uneconomic when concentrations of As reach several hundred parts per million. However, arsenic bearing nickel ore may be treated by blending with 'clean' ore sources, to produce a blended feedstock which the mill and smelter can handle with acceptable recovery.
The primary problem for treating niccolite in conventionally constructed nickel mills is the specific gravity of niccolite versus that of pentlandite. This renders the ore difficult to treat via the froth flotation technique. Within the smelter itself, the niccolite contributes to high arsenic contents which require additional reagents and fluxes to strip from the nickel metal.