Pyrite, bornite, haematite and covelline. Cornwall, Britain
250µm
Pyrite (pale yellow-white, bottom) is intergrown with bornite (brown-orange, left). This has altered along its grain edges to covelline (blue), which shows reflection pleochroism from light to dark blue (right centre). Rhythmically banded fine-grained haematite (green-grey, centre) surrounds the sulphides and shows slight differences in reflectance due to grain size variations (centre right). Quartz is dark grey.
Polished block, plane polarized light, x 80, air
