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Pedogenic alteration of illite in subtropical China

  • W. Han (a1), H. L. Hong (a1) (a2), K. Yin (a1), G. J. Churchman (a1) (a3), Z. H. Li (a4) and T. Chen (a5)...


Pedogenic alteration of illite from red earth sediments in Jiujiang in subtropical China was investigated using X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Illite, hydroxy-interlayered vermiculite (HIV), kaolinite and mixed-layer illite-HIV (I-HIV) are present in the soils. The characteristic reflections of the clay phases were 14 Å, 10–14 Å, 10 Å, and 7 Å, respectively. After Mg-glycerol saturations, the 14 Å peak of the samples did not expand, and after heating at 350°C and 550°C it shifted to 13.8 Å and 12 Å respectively, with no residual 14 Å reflection, suggesting the occurrence of hydroxy-interlayered vermiculite. The randomly interstratified I-HIV clays were characterized by a broad peak at 10–14 Å, which did not change its position after Mg-glycerol saturation, but collapsed to 10 Å after heating at 350°C and 550°C. HRTEM analysis showed different lattice fringes of 12 Å, 10 Å and 7 Å . Mixed-layer I-HIV, HIV-K and illite-kaolinite (I-K) were observed in the HRTEM images which represented the intermediate phases during illite alteration. The merging of two 10 Å illite layers into a 12 Å HIV layer, lateral transformation of one HIV layer into one kaolinite layer and alteration of one illite layer into two kaolinite layers illustrated the mechanisms of illite-to-HIV, HIV-to-kaolinite and illite-tokaolinite transformation, respectively. The proposed pedogenic alteration of illite and the weathering sequence of the clay minerals in Jiujiang is illite → I-HIV → HIV → HIV-K → kaolinite. In addition, illite may transform directly to kaolinite.


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Pedogenic alteration of illite in subtropical China

  • W. Han (a1), H. L. Hong (a1) (a2), K. Yin (a1), G. J. Churchman (a1) (a3), Z. H. Li (a4) and T. Chen (a5)...


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