华北第三系潞王坟组膨胀岩主要造岩矿物鉴定及微观特征研究

STUDY ON IDENTIFICATION OF MINERALS AND MICROSTRUCTURE ON N_(2l) SWELLING ROCK

华北上第三系泥灰岩和粘土岩都具有粘粒含量高及“半土半岩”的性质，具有遇水易崩解、膨胀的特性，呈弱～强膨胀潜势。以该区代表性膨胀岩为研究对象，通过X射线衍射实验（XRD）及电镜扫描（SEM）实验和能量光谱测试试验，分析膨胀岩土的造岩矿物的物质组成和微观结构特征。试验结果表明：泥灰岩含有非膨胀矿物方解石、石英、长石以及含有膨胀矿物蒙脱石、高岭土、伊利石等，矿物成分以方解石含量最高在38％～42％之间，其次为蒙脱石，含量在31％～35％之间。粘土岩同样含有以上矿物，但含量与泥灰岩有很大不同，粘土岩中蒙脱石含量35％～40％之间，而方解石的含量只有10％，远低于30％石英的含量。微观结构观察显示，泥灰岩中有少量方解石结晶体，局部富集半结晶的方解石，岩石中的粘土矿物呈层状局部褶曲，有溶蚀边，微细裂缝及孔洞少，而粘土岩中在电镜下未见方解石晶体，粘土矿物有大量褶曲，含大量微细裂缝及孔洞。

Neogene marl rock and clay rocks are of high content of clay and characteristic of ＂soil and rock＂,easy to collapse and expand in water with weak-strong swelling potential. XRD and SEM experiments and energy speetrium test are used to analyze rock-forming mineral compositions and mierostrueture of expansive soil. It shows that marl contains non-swelling mineral such as calcite,quartz, feldspar and also contains swelling mineral such as montmorillonite, kaolinite and illite. Of the non-swelling mineral,calcite has the highest content ranging from 38% to 42 %, followed by montmorillonite from 31% to 35%. Claystone contains similar mineral composition, but the content is different from marl with 35% -40% montmorillonite, and calcite of only 10%, much lower than 30 % of quartz. Microscopic study reveals that a small amount of calcite crystals exists in marl, with local enrichment of semi-crystallized calcite. Clay minerals in rocks possess partial folds and erosion edge, small micro-cracks and holes are also present.