Blaubleibender covelline, covelline, digenite and bornite. Mount Gabriel, County Cork, Ireland

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Digenite (light blue, little cleavage, bottom left of main sulphide) is extensively replaced about its margins by covelline (dark blue, centre left) and by coarse crystals of blaubleibender covelline. Blaubleibender covelline shows strong reflection pleochroism from blue-white (centre right of sulphide with good cleavage, oriented north-south) to medium blue (top left of sulphide with central polishing pits, oriented cast-west). Bornite (pink-brown, centre) also is being replaced by covelline. Minor amounts of malachite (light grey, centre) form veinlets cutting the sulphides. Euhedral feldspars (grey, top centre, bottom centre left) and quartz (grey, centre left) are associated with phyllosilicates (grey, poorly polished). Black areas are polishing pits.

Polished block, plane polarized light, x 80, air

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