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

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Very fine-grained haematite lies along the fabric of phyllosilicate grains (left). Both the green-white colour and incipient red internal reflections are characteristic of this type of fine-grained haematite. TiO2 (pink-brown) forms euhedral crystals with faint light-coloured internal reflections (bottom right), but is present as a rounded detrital grain that forms the light brown core (centre) to euhedral lanceolate haematite crystals (white, centre). The original iron-titanium oxide grain is now pseudomorphed by a fine-grained intergrowth of very minor haematite (white) and TiO2 (pink-white). Other white areas are haematite.

Grain mount, plane polarized light, x 180, oil

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