Wolframite and cassiterite. Glen Gairn, Scotland

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Euhedral cassiterite (grey, bottom centre) is twinned, shown by the differences in bireflectance (light and dark grey). Tabular wolframite (light grey-brown and grey-blue) is zoned, the inner zone is blue and the outer zone is grey-brown. Quartz (top left) and feldspar (bottom centre) show internal reflections, some of which are due to limonitic staining (orange, bottom right).

Polished thin section, plane polarized light, x 160, oil

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