Links between environmental conditions and pedogenic phyllosilicates in Podzols in the Tatra Mountains (Poland) : I. Mineralogy

Pedogenic minerals reflect the environmental conditions that prevailed during soil formation. The present study investigates the clay mineral composition of the fine clay fraction separated from four soil profiles in the Tatra Mountains, Poland. All profiles were developed from granitoids or granitic moraines and were classified as Podzols. The clay fraction (<0.2 μm) was separated from each soil horizon by centrifugation after removing carbonates, organic matter, and poorly crystalline iron phases through reactions with sodium acetate-acetic acid buffer, sodium hypochlorite, and citrate-bicarbonate-dithionite, respectively. The obtained clay fraction was then characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy, thermogravimetry, chemical analysis, and cation exchange capacity measurements. The dominant mineral in the studied samples was illite–smectite, followed by dioctahedral mica and kaolinite. Hydroxy-interlayering was observed within the mixed-layer minerals. Chlorite and gibbsite were also detected in some horizons. Selected XRD patterns were modeled using Sybilla software. Layer charge measurements of the expandable component of the samples indicated values corresponding to low-charge vermiculite/high-charge smectite, with these values being uniform for all investigated samples. The uniformity of the layer charge values may reflect the uniformity of the parent material or the uniformity of processes controlling the chemistry of the weathered part of the mica structure. The general absence of discrete smectite, despite the presence of kaolinite (and gibbsite), suggests that smectite may not be stable under the acidic conditions prevailing in the alpine Podzols of the Tatra Mountains.