Rutile, pyrite, marcasite, wolframite, cassiterite and arsenopyrite. Mount Pleasant, New Brunswick, Canada

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Rutile crystals (light grey, centre) show bireflectance (light to darker grey) and are rimmed by wolframite (brown-grey, bottom left) and fractured cassiterite (dark grey, top left, centre top) which has a markedly lower reflectance than rutile or wolframite. Euhedral cassiterite crystals occur within the gangue between rutile and pyrite-marcasite aggregates (centre top) and show internal reflections (top centre). Pyrite (light yellow-white, bottom right) and marcasite (blue-green white, centre top right) are intimately intergrown (right) and have replaced pyrrhotite. A euhedral crystal of arsenopyrite (white, high reflectance, top left) is present in the silicate gangue (black).

Polished block, plane polarized light, x 160, oil

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