By means of transmission electron microscopy (TEM), the study on hypersthene megacryst and uralitized hypersthene from anorthosite complex of Chengde, Hebei Province of China shows that the layer silicate minerals such as talc and smectite would grow on the (100) under the con- dition of supergenesis. This kind of silicate is the product of the polysomatic reaction, and their evolution of growth from small to big was observed by TEM. In most cases, the layer silicate nucleus in the form of rhomb block firstly grow out of the interfaces of the augite exsolution lamellae in the hy- persthene matrix. The boundary faces of the rhomb blocks are parallel to {210} of hypersthene. The small blocks could link each other in the form of veins, and further in the form of flakes. It is proposed that the growth of layer silicates is constrained by the nucleation mechanism of polysomatic reaction. The characteristics of the super-microstructure for the uralitized hypersthenes show that the polysomatic reac- tion from pyroxene to amphiboles is caused by the bulk reac- tion mechanism.
XPS and AES depth composition profile studies were carried on to understand chemical components of (100) surfaces for Chengde hypersthene from Hebei Province, China, and Bamble enstatite from Norway. Also, to understand the microtopography of them the AFM observation was carried on. There are obvious differences between chemical components of (100) surface and those of mineral inner. Compared with inner mineral Si4+ proportion in total cations has no distinguished variation, whereas Ca2+ and Al3+ proportions increase respectively, and Mg2+ proportion decreases. AES depth composition profile of 2000s shows that at a depth of 70 nm the atomic concentrations (%) for each element (except Si in Chengde hypersthene) slightly go up and down, but the average values have no obvious change. On the profile, the atomic concentrations (%) of Al and Si for Chengde hypersthene present a compensated relationship. Obviously, the Si and Al must have the relationship of isomorphic replacement on the (100) surface. The image of AFM shows that there is hillock growth on the (100) surface in the layered form of the polygon with 0 to several hundreds nm in thickness. The growth is a sort of secondary phyllosilicate minerals. The observation of the above-mentioned phenomenon and the recognition on the above regularities are benefit for understanding of the mechanism for weathering and water-rock reactions.
XUE Jiyue, PAN Yuguan, LUO Gufeng & LU HaipingDepartment of Earth Sciences, Nanjing University, Nanjing 210093,ChinaCorrespondence should be addressed to Xue Jiyue (e-mail: xuezhou@nju.edu.cn)
