A DICKITE WITH PARTICULAR MORPHOLOGY FOUND IN XUZHOU COAL BASIN

A dickite with an elogated crystal habit in the direction of the a-axis occurs as pore fillings in coarse quartzite sandstone of Upper Permian Shiqian-feng Formation in Xuzhou coal basin,Jiangsu province.Scanning electron microscope micrographs of the dickite clearly show euhedral crystal outlines. The length of its plates is from 25 to 40μm and the width 4μm;The ratios of the length and width varies from 6:1to 10:1.Elogated pseudohexagonal flakes commonly stacked in book-like assemblages.Results of thin section observation, X-ray diffraction pathern,infrared spectrum and different thermal analysis confirm it as a dickite.It was precipitased from pore fluids after the overgrewths of quartz formed Log (Al ) -PH solubility diagram was constructed and indicated that the dickite was formed in acidic environment. The particular morphology with elogated crystal habit probably was caused by dilute porewater and slow crystalization.