argillans

Argillans are thin coatings of clay minerals that line the interior surfaces of soil pores and cracks. They are a pedogenic feature produced when clay particles are mobilized in the soil solution and deposited on the walls of pores as suspensions move downward or laterally through the soil profile. The result is cohesive films or skins of clay, sometimes forming along root channels or in cracks, which may appear as glossy or dull films and can be colorless or colored by iron oxides.

Argillans form in soils with sufficient supply of clay fractions and under moisture regimes that promote clay translocation, such as during cycles of saturation and drying or in zones with a fluctuating water table. They are commonly observed in illuvial horizons or in hydromorphic soils where illuviation is active, and they may accompany other pedogenic features such as soil mottling, vertic properties, or gleying.

In soil properties, argillans reduce pore space and can modify hydraulic conductivity locally. They are diagnostic of clay translocation in some soil classification schemes and help indicate the developmental stage of a soil profile. Their appearance can range from delicate films that coat small pores to more substantial clay skins lining larger voids.

Argillans are primarily of interest to soil scientists and geotechnical engineers as indicators of soil formation processes and as factors influencing drainage and aeration in clays-rich soils.