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.
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.
While this was originally an alternative concept, increasing mainstream research has been devoted to soil amendment and other benefits of rock flour application: for instance, a pilot project on the use of glacial rock, granite and basaltic fines by the U.S. Department of Agriculture at the Henry A. Wallace Beltsville Agricultural Research Center. The SEER Centre in Scotland is a leading source of information on the use of rock dusts and mineral fines. The Soil Remineralization Forum was established with sponsorship from the Scottish Environment Protection Agency and has commissioned a portfolio of research into the benefits of using mineral fines. The Forum provides an interface between research, environmentalists and industry.