Silt it is a name given to a range of particle size. It is usually considered to be material between 2 micrometers (microns) and 20 micrometers (although the upper limit is given in othe classification schemes as 50 or 63 micrometers). Silt sized material can occur in soils as well as rivers or deltas or in the deep sea. It is larger than clay-sized material but smaller than sand. Silt can be produced in a number of ways: weathering of rocks, grinding by glaciers, aeolian abrasion as well as water erosion of rocks on the sides or beds of rivers. Silt is easily transported in water or air 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).