Sphalerite, chalcopyrite, pyrite, galena and covelline. Parys Mountain, Britain

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Chalcopyrite (yellow, top right) is intergrown with sphalerite (light grey, centre). Sphalerite is fractured and partially replaced by covelline (blue, bottom centre). Euhedral pyrite (light yellow, high reflectance, top left) is intergrown with galena (blue-white, top centre). Widespread replacement of sphalerite by chalcopyrite (as chalcopyrite disease) is crystallographically controlled (centre right) or very fine-grained so giving a yellow-brown surface colour to the sphalerite (centre left), black areas are voids.

Polished block, plane polarized light, x 80, air

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