what is loess

Loess is a type of sedimentary deposit that is predominantly silt-sized and formed by the accumulation of wind-blown dust. It is defined as an accumulation of 20% or less of clay with a balance of roughly equal parts sand and silt, often loosely cemented by calcium carbonate. Loess is homogeneous, porous, friable, pale yellow or buff, slightly coherent, typically non-stratified, and often calcareous. It has vertical capillaries that permit the sediment to fracture and form vertical bluffs. Loess grains are angular, with little polishing or rounding, and composed of quartz, feldspar, mica, or other mineral crystals. Loess covers about 10% of Earths land area and is most widespread in todays temperate zones and in the marginal semiarid zones of the deserts. Loess usually exhibits a surface cover of fertile soil that is conducive to intensive agriculture. The lithological classification of loess is based on physical and chemical properties, and the conditions of origin are partly or entirely neglected. Loessial deposits include sandy loess, loessial sand, loess loam, clayey loess, and loess that is altered during soil-forming processes. Loesslike deposits, on the other hand, include sediments that resemble typical loess only in certain features (mineralogical composition, dominant dust fraction, color, etc.) .