Pyrite, graphite and marcasite. Strontian, Scotland

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Subhedral crystals of pyrite (yellow-white, centre) are intergrown with minor lath-shaped aggregates of marcasite (white, centre top) which are pseudomorphs after pyrrhotite. Graphite laths (brown, low reflectance) show faint bireflectance. Garnet (light grey, top right), biotite (lith-shaped, bottom left), plagioclase and quartz (featureless) are the main silicates.

Polished thin section, plane polarized light, x 80, air

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