Virtual Atlas of Opaque and Ore Minerals
Haematite and TiO2 minerals. St Bees Sandstone. Cumbria, Britain
Haematite occurs as very fine crystals (right) that lie along the basal cleavage of phyllosilicates; as martite (blue-white, bottom centre); as a medium grained mosaic (top left) and as authigenic lanceolate euhedral crystals (top left) overgrowing detrital haematite. Haematite shows faint bireflectance and reflection pleochroism from blue-white to white (top left). A detrital TiO2 mineral (light grey-brown, top right) is porous and is enclosed within two well crystalline TiO2 overgrowths. The junction between the two rims is seen as a thin line of trapped silicates (dark).
Grain mount, partially crossed polars, x 160, oil