Loess (US: , UK: ; from German Löss [lœs]) is a clastic, predominantly silt-sized sediment that is formed by the accumulation of wind-blown dust. Ten percent of the Earth's land area is covered by loess or similar deposits.Loess is an aeolian (windborne) sediment being an accumulation of: twenty percent or less clay and the balance mainly equal parts sand and silt typically from 20 to 50 micrometers per particle often loosely cemented by calcium carbonate. It is usually homogeneous and highly porous and is traversed by vertical capillaries that permit the sediment to fracture and form vertical bluffs.