The kaolinite rock, 2-6 m thick, occurs 6-19 m below NO. 4 coal seam at the bottom of Xiashihezi Formation, being a stable correlation key bed in a large area. The pelletoid kaolinite rock, formed in the lacustrine environment of delta plain, is an important type of rock. Six texture types of pellets are identified:Concentric pellets without nuclei, pellets with nuclei, radial pellets, laminae-free pellets,irregular pellets, transitional pellets. Organic matter, derived from strong degradation of algae, are amorhpous and yellow-green under fluorescence, and play a great role in the formation of pellets. The clay particles suspended in the water are linked by organic matter, forming aggregates, then sinking and rolling under the influence of water current on the bottom of basin, thus forming various types of pellets. The concentric texture is also related to the seasonal change. There are two genetic kinds of kaolinite:One is the terrigenous clay minerals, transported and deposited in the lacustrine basin, which show rounded and irregular shape, The other is precipitated by alumino-silicate gels and recrystallized in the diagenesis stage, which show radial arrangment and well hexagonal flake shape.