Distinctive features of chemical components and minerals in mass and clay portions of completely decomposed granite

Abstract

In chemical and mineral tests on the completely decomposed granite, the mass specimen and the clay portion (particle diameter <2 μm) were to be undertaken. It was well known that the two parts played different roles in soil engineering geological behaviors because of their distinctive material constituents and microstructures. The correlation of the two parts was seldom clarified in previous studies. With the purpose of identification of weathering grades in detail, comparison of mineral components, chemical constituents in the two parts and analysis of their relationships, tests on the mass and the clay portions of the 6 completely decomposed granites were carried out, which included sieve analysis and sampling pipette on the particle size distribution, X-ray fluorescence spectrum of sequence-type on chemical components, and X-ray diffraction on mineral constituents. By comparison, it was found that for these gravel-bearing soils, the content variation of chemical components was closely concordant with that of mineral proportions, especially those of clay minerals. When compared with those in the mass, it was disclosed that the content of SiO2 in clays decreased nearly 50%, K2O was also lessened, while the contents of Al2O3, Fe2O3 and H2O+ had an obvious increasing. For these chemical components, most of them increased. In mineral components, the quartz, clay minerals and feldspar account for the majority in the mass, and the halloysite and kaolinite were dominant in clays, the next being illite. Among the correlations of particle size, chemical contents and mineral proportions, the significant relations existed between quartz and gravel with positive relation, quartz and sands with negative relation, feldspar and sands with positive relation, clay minerals and Al2O3, loss of ignition (LOI) with positive relations, respectively. The halloysite in clays and clay minerals in the mass were positively related with each other.