Pyrite, rutile, columbite and zircon. Greisenized granite. Ririwai, Nigeria
250µm
Rutile (pale blue-grey, centre right) encloses slightly lower reflectance columbite (brown-grey, centre right) cores in a characteristic association. The blue surface colour of rutile is associated with its deep blue internal reflections. Subhedral to euhedral pyrite (yellow, high reflectance, centre) surrounds rutile and shows alteration to limonite (poorly polished areas of pyrite, bottom right). Zircon (medium grey, slightly higher reflectance than quartz) is rounded to subhedral and two grains lie within rutile crystals (centre right) or discretely between pyrite and rutile (centre bottom). Although the reflectance of zircon is lower than columbite, it is higher than the silicates. The main silicate is quartz (left) accompanied by phyllosilicates (poorly polished, lower reflectance, centre top). Black areas are polishing pits.
Polished block, plane polarized light, x 80, air
