Cassiterite, ilmenite and columbite. Jos Plateau, Nigeria

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This is a concentrate from a river placer comprising a mixture of oxides. Cassiterite (grey) is twinned (bottom right) and shows bireflectance, faint reflection pleochroism and faint internal reflections (red, bottom left). It is intergrown with columbite (light brown-grey, bottom right), which has a slightly lower reflectance than ilmenite (pink-brown, left centre). Ilmenite has altered along its edge to a mixture of poorly crystalline haematite and TiO2 (blue-grey, left centre).

Grain mount, plane polarized light, x 180, oil

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