Cassiterite and zircon. Microclinized granite. Ririwai, Nigeria
Cassiterite crystals (light grey, highest reflectance, many polishing pits) are twinned (centre right) as shown by their bireflectance variations. Cassiterite is intergrown with subhedral to euhedral zircon (medium grey), which is zoned with thin lower reflectance outer rims (centre left, left). A little pyrite (pale yellow, high reflectance, bottom) is present. The main silicates are quartz (right) and feldspar (bottom left). Black areas are polishing pits.
Polished block, plane polarized light, x 80, air