Ilmenite, TiO2-rich minerals and haematite. Derbyshire, Britain
Two laths of ilmenite show widespread to complete alteration. The central lath comprises a number of ilmenite crystals (light to darker brown, centre) which show reflection pleochroism and bireflectance (centre). Alteration is extensive and two main 'phases' are present: TiO2-rich areas (light brown-grey, centre) and a higher reflectance 'phase' which is a mixture of haematite plus minor TiO2-rich minerals (cream-white, centre). The more altered ilmenite lath (top left) now consists of a very fine-grained porous mixture of haematite and TiO2-rich minerals. The silicates are subhedral pyroxene (grey, bottom left) and plagioclase (dark grey to black and featureless). The orange area is due to stray internal reflections within the silicates. At higher magnification in oil, the fine-grained alteration products can be more easily resolved.
Polished block, plane polarized light, x 160, oil