Haematite, oxidized magnetite and chalcopyrite. Derbyshire, Britain

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Skeletal magnetite crystals (cruciform-type, brown-white, centre left) and ilmenite laths (brown-white, right centre) are intergrown with lath-shaped plagioclase (centre left) and equant pyroxene (both light grey) and poorly polished clay minerals (dark grey), some of which have pseudomorphed olivine. Both magnetite and ilmenite have oxidized with a lightening of their surface colour. Fine-grained haematite (white, poorly polished, centre) has partially pseudomorphed olivine (centre) and also forms veinlets cutting across the silicates. Very fine-grained haematite has a characteristic green-brown colour which is partially due to red internal reflections. A small crystal of chalcopyrite (yellow, high reflectance, centre top) is present close to two polishing pits (black, centre top).

Polished block, plane polarized light, x 80, air

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