徐州石炭-二叠系中首次发现一种特殊形态的地开石

徐州煤田上二叠统石千峰组地层底部粗粒石英砂岩中,发现了晶体沿a轴方向延伸的假六方板条状粘土矿物。扫描电镜观察到清晰的单体形态轮廓,片体长一般约25μm,最长达40μm,宽约4μm,长宽比为6∶1-10∶1板条状片体面对面叠置成“书册”状集合体,聚集在砂岩孔隙中。薄片光性观察、X射线衍射分析、差热分析和红外光谱分析证实为地开石。这种特殊形度的地开石是从孔隙沉淀中直接沉淀的。缓慢地结晶速度是地开石形态变化的主要原因。

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.