Short-Term Changes in Test-Biotite of Various Particle-Size Fractions as Affected by the Current Pedogenesis in a Podzolic Soil
A model field experiment was performed with clay-sized (<1 μm) and medium silt-sized (5–10μm) test-biotite to examine the changes in the test-mineral after one year and three years of incubation in the AELoa horizon of a podzolic soil. After one year, the test-biotite in both size fractions was partially transformed into irregular mixed-layered biotite–vermiculite. After three years, the most part of the initial test-mineral was transformed into irregular mixed-layered biotite–vermiculite, irregular biotite–vermiculite–pedogenic chlorite, and small amounts of vermiculite and pedogenic chlorite. The formation of expandable minerals from biotite was accompanied by the reducing layer charge and by the loss of interlayer potassium and octahedral Mg and Fe. A deeper transformation was observed in silt-sized biotite as compared with clay-sized biotite. This trend was confirmed by the fact that the decrease in the proportion of nonexpendable biotite layers in the mixed-layered minerals and the reduction in the thickness of mineral crystallites were more evident in silt-sized test-mineral particles.