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The presence and formation of hydroxy-interlayered minerals in the Holocene paleosol at the Wugong profile on the southernmost Chinese Loess Plateau were investigated by examining the < 1 μm and 1–2 μm clay fractions of the 50–150 cm horizon by Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). Prior to the analyses free Al and Fe phases were removed by dithionite-citric-bicarbonate (DCB) extraction. XRD patterns were obtained with air-dried, Mg-saturated, Mg-saturated with glycerol solvation (Mg-glycerol) and K-saturated and heated at 110, 250, 350, 450 and 550 °C samples both before and after hydroxy-interlayered materials removal by sodium citrate extraction. The absorption bands at 3699 and 3430 cm − 1 in the FTIR spectra of both sub-fractions indicated the presence of hydroxy-interlayered minerals. The K-saturated and heated XRD patterns confirmed this by the progressive collapse of the 1.4 nm reflection to a 1.0 nm reflection. After removal of the hydroxy-interlayered materials no obvious increase of the relative XRD intensity of the 1.8 nm reflection in Mg-glycerol pattern was observed and the 1.4 nm reflection exhibited a stronger collapse to 1.0 nm after K-saturation and increasing temperature treatment. This indicated that the hydroxy-interlayered minerals in the Holocene paleosol were mainly composed of hydroxyl-interlayer vermiculite. The hydroxyl-interlayer vermiculite was formed by the polymerization of Al/Fe-hydroxy materials within the interlayer space of vermiculite. Shoulder-like reflection at 1.2 nm in the K-550 °C pattern of the 1–2 μm fraction indicated a higher degree of Al/Fe-hydroxylation in the coarse fraction than in the fine fraction, which was consistent with the lower extractable Al and Fe in the coarse fraction. The reflection at 1.38 nm in the K-550 °C pattern could be interpreted as pedogenic chlorite. Thus, transformation of vermiculite into hydroxy-interlayered vermiculite and finally into a chlorite-like mineral (pedogenic chlorite) has occurred in the Holocene paleosol on the southernmost Chinese Loess Plateau. [ABSTRACT FROM AUTHOR]

Despite extensive researches, many aspects of the structural transformation that occur in illite on heating remain unclear. This study concentrates on samples from a mine located in Wenzhou, Zhejiang Province, China to supplement data obtained by previous investigators. In situ high temperature X-ray diffraction (HTXRD), infrared spectroscopy (IR), field emission scanning electron microscope (FESEM) and electron microprobe (EMP) analysis were used to record the characterization of the raw material. XRD pattern showed the illite sample was primarily in 2M 1 polytype. The phase transition from illite into dehydroxylated phase started at about 525 °C in static air and at about 550 °C in vacuum, and from dehydroxylated phase into mullite occurred at above 1100 °C. These lattice parameters of illite (RT – 1100 °C) and mullite (1125–1150 °C) both in static air and in vacuum were refined. The variations of illite lattice parameters with temperature (°C) were therefore well described. Thermal expansion coefficients of illite (RT – 1100 °C) were determined. In situ high temperature X-ray diffraction study revealed four stages during heating: expansion, dehydroxylation, post-dehydroxylation and mullite stages. [ABSTRACT FROM AUTHOR]