Wang YongJin;Yang Hao;Gao WenLi;Wang YJ;Yang H;Gao WL

;Department of Geography, Nanjing Normal Univ., Nanjing 210097, China.

particle size distribution;particle size;kaolinite halloysite weathering granite soil parent materials;soil formation;minerals electron microscopy;x ray diffraction;indexes soil types;granite soils;china jiangxi

The kaolins collected from a profile of weathered granite at Yichun County, Jiangxi Province, China, were subjected to particle size fractionation by the conventional sedimentation method and examined by x-ray diffraction, scanning and transmissionelectron microscopy. All of them exhibited a mixture phase of poorly crystallized kaolinites and halloysites (0.7 nm) occurring as the main clay minerals. Electron micrographs showed that plate kaolinites were the principal constitution in the coarse fraction, with more tubular and curled halloysite (0.7 nm) in the fine fraction. Both of them showed normal probability curves in particle size distributions. The ratios of kaolinite and halloysite (0.7 nm) in different size fractions were examined by X-raydiffraction with a series of X-ray patterns characterized by three main peaks at d(001), d(002), and d(020), varying in intensity. An index, Qhm, expressed as (Id(001) + Id(002))/(2 X Id(020)) was 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 micro-environments, the index Qhm could be used to indicate weathering and pedogenic conditions of a weathering crust.