Silt

Silt refers to soil or rock particles of a certain very small size range (see grain size). Silt particles fall between 0.004 and 0.063 mm (4 - 62.5 μm). A silt particle is larger than a clay particle but smaller than a sand grain. At least up until 1980, the U.S. Army Corps defined silt as particles smaller than 0.074 mm.

Silt can occur as a deposit or as material transported by a stream or by a current in the ocean. Silt can be produced in a number of ways: weathering of rocks, grinding by glaciers, aeolian (wind) abrasion as well as water erosion of rocks on the bedss of rivers and streams. Silt is easily transported in water and is fine enough to be carried long distances by air as 'dust'. Thick deposits of silty material resulting from aeolian deposition are often called loess (a German term) or limon (French). Silt and clay contribute to turbidity in water.

See also sediment.