Thorite, cassiterite and zircon. Greisenized granite, Ririwai, Nigeria

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Two aggregates of thorite crystals have very strong red-orange internal reflections due to very fine-grained haematite inclusions. This is the characteristic feature of thorite from these rocks. Although few surface features are discernible, the core (oriented cast-west) of the right hand aggregate is relict zircon. Cassiterite (light greys) is euhedral to subhedral and twinned (top centre). The light yellow, poorly polished area (bottom right) is brass within a polishing pit. A zircon with strong internal reflections lies below it.

Polished thin section, plane polarized light, x 160, oil

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