Short-Term Changes of Biotite in Various Particle-Size Fractions of Podzolic Soil in a Model Field Experiment

Resumo

An experiment on the transformation of test biotite of the clay fraction (<1 µm) and the medium silt fraction (5–10 µm) immersed into the AELоа horizon of podzolic soil for one or three years was performed. Partial transformation of biotite in the medium silt and clay fractions into irregular biotite–vermiculite under the modern pedogenesis conditions within one year of incubation in the AELоа horizon of podzolic soil was demonstrated. A considerable part of biotite was transformed into irregular biotite–vermiculite and biotite–vermiculite–pedogenic chlorite, and small amounts of vermiculite and pedogenic chlorite were formed after three years of incubation in the soil. Biotite transformation into expandable minerals was accompanied by the decrease in the layer charge, loss of interlayer K, and loss of Mg and Fe from the octahedral lattice. Mica transformation was most significant in the medium silt fraction: the overall decrease in the share of nonexpandable biotite layers and in the thickness of biotite crystallites after three years of incubation was more pronounced in this fraction than in the clay fraction.