These specimens, originating from the Nanisivik Mine on Baffin Island, Nunavut, are considered some of the finest examples of grimmite ever found. The crystals appear as prismatic, bright grey needles that coat chalcopyrite crystals, they are associated with chalcopyrite, and are often accompanied by micro chalcocite. Analysis by Dr. Andrew Locock at the University of Alberta confirmed the composition as NiCo₂S₄. In some grains, a core of chalcopyrite is overgrown by grimmite, highlighting the complex mineralization.
The nomenclature of Ni-Co thiospinels was revised recently and now includes:
Although NiCo₂S₄ (grimmite) had been poorly defined for years, with some authors previously grouping it under siegenite, its distinct identity was finally established in 2020. While grimmite is not an uncommon member of the linnaeite group, it is notably rarer than siegenite.
The Nanisivik Mine, situated 750 km (470 miles) north of the Arctic Circle, operated from October 15, 1976, until its closure in September 2002 due to declining resources and low metal prices. Primarily a zinc-lead operation producing sphalerite as its main ore, the mine also gained prominence for yielding unique and high-quality mineral specimens. These grimmite specimens stand as remarkable and well-preserved examples from this historic, long-closed zinc mine.
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