Sphalerite, cassiterite, thorite and zircon. Greisenized granite. Ririwai, Nigeria

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Sphalerite (light-grey, left) is inclusion-free and has a reflectance slightly greater than cassiterite (light-grey, centre right). Two irregular thorite crystals (dark grey, centre bottom, one with a central polishing pit, bottom centre) have low reflectance; higher reflectance areas are due to fine-grained haematite inclusions. Zircon crystals are euhedral (bottom left) and have a reflectance greater than thorite but less than cassiterite. Quartz (dark grey, well polished, bottom left) and micas (lower reflectance and poorly polished) are the main silicates. Black areas are polishing pits, some of which contain grinding grit (centre top). At this magnification the identification of the accessory phases is difficult.

Polished thin section, plane polarized light, x 40, air

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