Rock flour, or glacial flour, consists of clay-sized particles of rock, generated by glacial erosion or by artificial grinding to a similar size. Because the material is very small, it is suspended in river water making the water appear cloudy. If the river flows into a glacial lake, the lake may appear turquoise in color as a result. Examples of this are Lake Louise and Peyto Lake in Canada and Gjende lake in Norway. Formation Natural rock flour is typically formed during glacial migration, where the glacier grinds against rock beneath it, but is also produced by freeze thaw, where the act of water freezing and expanding in cracks helps break up rock formations. Although clay-sized, its particles are not clay minerals but typically ground up quartz and feldspar. Rock flour is carried out from the system via meltwater streams, where the particles travel in suspension. Rock flour particles can travel great distances either suspended in water or by the wind, in the latter case forming deposits called loess. EXTRACT from Wikipedia under ROCK FLOUR definition.