Haematite, TiO2 minerals and zircon. St Bees Sandstone. Cumbria, Britain

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Haematite as martite pseudomorphs after magnetite (two crystals, centre right) and as a rounded lath-shaped pseudomorph (bottom centre) is white and shows faint bireflectance (blue-white to white, centre right). Fine-grained haematite (centre left) is green-blue and is accompanied by incipient red internal reflections. TiO2 (pink-grey, bottom centre) forms an authigenic overgrowth around the detrital haematite pseudomorph, and a discrete triangular detrital grain (top right). Two zoned zircon crystals (centre and top right) are grey and have low reflectance, and show faint red internal reflections due to very fine haematite inclusions. The central zircon has a higher reflectance core and lower reflectance rim.

Grain mount, plane polarized light, x 180, oil

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