Crystal System: Orthorhombic
Status of Occurrence: Confirmed Occurrence
Chemical Composition: Nickel arsenide
Chemical Formula: NiAs2
Method(s) of Verification: Dolyhir Quarry - optical properties in polished section (R.A. Ixer, unpublished data).
Introduction: rammelsbergite belongs to the lollingite group of diarsenide minerals - lollingite being the iron-bearing member. Rammelsbergite is sometimes present as a minor phase in hydrothermal base-metal sulphide bearing mineral veins. It tends to occur more abundantly in the nickel-cobalt-silver-arsenic-bismuth (Ni-Co-Ag-As-Bi) 'five-metals' association, when it is usually intergrown with other Co-Ni arsenides and sulpharsenides. Rammelsbergite is, unusually for Fe-Co-Ni arsenides, straightforward to identify in polished section, exhibiting distinctive interference colours (brown/purple) when viewed under partly crossed polars.
Occurrence in Wales: although the \"five-metals\" association is absent from Wales, rammelsbergite has been found during recent reflected light petrological studies of base-metal sulphide bearing vein mineralization which formerly outcropped at Dolyhir Quarry in the Welsh Borders.
- Dolyhir Quarry, Old Radnor, Powys: microscopic rammelsbergite has been noted as a component (R.A. Ixer, unpublished data) of a tennantite + galena + chalcopyrite dominated polymetallic vein assemblage, from a rib of massive intergrown sulphides which was exposed in the quarry during the mid 1990's and has since been quarried away. Many samples of the sulphide mineralization were preserved at the National Museum of Wales, however, and work continues on characterising the primary mineralization. More information on the occurrence of rammelsbergite in this assemblage will be posted as it becomes available.
There are no key localities for this specimen.
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