Cassiterite and wolframite. Glen Gairn, Scotland

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Cassiterite (light grey, top left and right) is euhedral and zoned (top right). This zoning is shown by differences in reflectance. Wolframite (centre) is simply twinned and zoned with an inner zone which has altered to fine-grained poorly polished scheelite, enclosed within unaltered wolframite. A thin outermost zone also shows alteration to scheelite and hence is less well polished. Quartz is featureless and feldspar shows minute opaque phases and fluid inclusions along its cleavage (top left).

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

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