Nickeline

Crystal System: Hexagonal
Status of Occurrence: Confirmed Occurrence
Distribution: Rare
Chemical Composition: Nickel arsenide
Chemical Formula: NiAs
Method(s) of Verification: Great Orme Copper Mines - EMPA (Parnell, 1988).

Chemical Group:

  • Sulphides

Geological Context:

  • Igneous
  • Hydrothermal: Mississippi Valley Type veins
  • Hydrothermal: epithermal polymetallic veins & pipes
Introduction: nickeline (also known as niccolite) is found most commonly in massive magmatic sulphide deposits and in silver deposits where it is associated with other Ni-Co arsenides and native silver. Neither of these associations are known from Wales. It may, however, occur as a trace mineral in other types of ore deposits.
Occurrence in Wales: nickeline is only known from a single locality in Wales. However, this is perhaps unsurprising as the classic nickeline-bearing associations do not feature in the otherwise considerable diversity of Welsh mineral deposits.

Key Localities:

  • Great Orme Copper Mines, Llandudno, Gwynedd: cobaltian nickeline with the formula (Ni0.82Co0.18)0.95As has been identified as microscopic grains occurring on fractures within uraniferous hydrocarbon from the Ty Gwyn section of these mines (Parnell, 1988).

References:

  1. Parnell, J., 1988. Mineralogy of uraniferous hydrocarbons in Carboniferous-hosted mineral deposits, Great Britain. Uranium, 4, 197-218.