Galena, native gold and pyrrhotite. Clogau Mine, Wales, Britain

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Galena (blue, centre top) is intergrown with native gold (yellow, high reflectance, centre bottom). Pyrrhotite (brown, hard, centre) crystals are enclosed within galena. Quartz (black) is the main gangue The apparent surface colour and reflectance of galena, and to a lesser extent pyrrhotite are altered by the optical properties of the gold, which is 950 fine. The gold shows fine scratches and minute immersion oil droplets (grey), which almost look like crystallographically controlled fine-grained inclusions.

Polished block, plane polarized light, x 80, air

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