Haematite, chamosite, limonite and TiO2 mineral. Egypt
An irregular-shaped chamosite core (green internal reflections, right) is surrounded by haematite (blue-white) bands where individual haematite crystals lie along the bands. Limonite (blue-grey, top centre) shows faint orange internal reflections which are stronger in smaller limonite crystals (top left). An angular clast of a TiO2 mineral (white, centre left) has higher reflectance than haematite. Chamosite ooids (bottom left, top centre) have concentric bands of chamosite (yellow-green internal reflections). In thin section, most of the ooids show pseudo-uniaxial crosses which suggest that their chamosite crystals are radially oriented. The matrix is limonite and limonitically-stained chamosite (brown chamosite in thin section).
Polished block, plane polarized light, x 160, oil