Haematite and magnetite. Skye, Scotland
Haematite (white, right) is coarse-grained and shows very faint bireflectance along (101 1) twin planes, which are oriented north-south but difficult to see in plane polarized light. Magnetite (pink-brown, bottom left) is well polished. Dark grey areas are silicates, black areas are polishing pits.
Polished block, plane polarized light, x 80, air