Arsenopyrite, chalcopyrite, cassiterite, sphalerite, stannite group minerals and covelline. Devon, Britain




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250µm


Arsenopyrite (white, high reflectance, top right) is the main phase; some is extensively fractured and cemented by chalcopyrite (yellow, centre left), which is altered to covelline and rimmed by brown stannite. Two euhedral cassiterite crystals .(grey, centre) are surrounded by stannite (brown-grey, centre) and covelline (blue, centre, left). Sphalerite (pale grey, right) is intergrown with arsenopyrite. Black areas are polishing pits.


Polished block, plane polarized light, x 80, air



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