Occurrence and characteristics of layer silicates in alluvial soils from the Lower Wisła river valley, Poland

The mineralogy of clay fractions (2 μm) separated from 4 pedons of alluvial soils (Fluvisols) was investigated to determine the distribution of layer silicates with depth and to examine the type of ordering of illite/smectite minerals, as well as the content of smectite layers. The dominant minerals are illite, smectite and mixed-layer illite/smectite. Chlorite, kaolinite and vermiculite were also identified. The percentage of smectite layers in the illite/smectite mixed-layered phase (swelling) ranges from 38% to 79%. Interstratification is ordered to some degree but randomly oriented illite/smectite were also detected. The amounts of smectite and mixed-layer illite/smectite tend to increase with depth in profiles. Soils in surrounding parts of the catchment consisted mainly of illite indicating, that with increasing time of soil formation, illite transforms to smectite via mixed-layer illite/smectite in alluvial soils.