Pedosphere 7(3): 211--218, 1997
ISSN 1002-0160/CN 32-1315/P
©1997 Soil Science Society of China
Published by Elsevier B.V. and Science Press
Particle size distribution of kaolinite and halloysite in weathering products of granite and its implications for pedogenesis
WANG Yong-Jin1,2, YANG Hao2 and GAO Wen-Li1
1 Department of Geography, Nanjing Normal Univ., Nanjing 210097 (China)
2 LMCP, Institute of Soil Science, Academia Sinica, Nanjing 210008 (China)
ABSTRACT
      The kaolins collected from a profile of weathered granite at Yichun County, Jiangxi Province have been subjected to particle size fractionation by the conventional sedimentation method and examined by XRD, SEM and TEM. All of them exhibit a mixture phase of poorly crystallized kaolinites and halloysites (0.7 nm) occurring as the main clay minerals. Electron micrographs reveal that plate kaolinites are the principal constitution in the coarse fraction, and more tubular and curled halloysite (0.7 nm) in the fine fraction. Both of them show normal probability curves in particle size distributions. The ratios of kaolinite and halloysite (0.7 nm) in different size fractions are examined by X-ray diffraction with a series of X-ray patterns characterized by three main peaks at d(001), d(002) and d(020),varying in intensity. Therefore, an index Qhm expressed as (Id(001) + Id(002))/(2×Id(002)), is designed to indicate relative ratios of the two clay minerals in a number of mixture phases. Because kaolinite and halloysite (0.7 nm) commonly occurred, respectively, in low and medium leaching microenvironment, the index Qhm, can be used to indicate weathering and pedogenic conditions of a weathering crust.
Key Words:  kaolin-group minerals, particle size distribution, weathering crust
Citation: Wang, Y. J., Yang, H. and Gao, W. L. 1997. Particle size distribution of kaolinite and halloysite in weathering products of granite and its implications for pedogenesis. Pedosphere. 7(3): 211-218.
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