Sphalerite, pyrite and chalcopyrite. Aarja, Oman

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Sphalerite (grey, top left) forms botryoidal aggregates upon poorly crystalline pyrite (light yellow, top left). Euhedral sphalerite crystals (centre) have a hexagonal-looking morphology suggesting that they were initially wurtzite. Coarse discrete pyrite crystals are unzoned and euhedral (centre), whereas fine crystals within a northeast-oriented vein have lower reflectance cores. Chalcopyrite (yellow, bottom right) is intergrown with pyrite and rimmed by sphalerite. The sphalerite is free of chalcopyrite disease. Quartz is dark grey, black areas are polishing pits.

Polished block, plane polarized light, x 80, air

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