Polozhikha River placer deposit, Rezhevsky District, Sverdlovsk Oblast, Russia
Polozhikha River placer deposit is in alluvial gravel-sand layers (0.1 to 1.2 m thick) on the floodplain and on terraces above the floodplain. The smooth rock floor of the placer deposit in its upper and middle parts is gneiss with intercalations of micaceous schists, granite dikes and bodies of amphibole-chloritic rocks. The lower part of the placer deposits have a rock floor of marble with numerous cracks and depressions.Corundum is irregularly distributed and forms enriched strips - "jets", which extend along the stream profile. Equidimensional grains of rubies and blue, light blue and colourless sapphires (1.5 to 6 mm) are present in the placer deposit. Larger grains are characteristically flat or elongate in shape.
Ref: E. Ya. Kievlenko, Geology of gems, 2003, p. 62