Mineral Composition and Microstructure of Completely Decomposed Migmatitic Granite

The microstructure of completely decomposed migmatitic granite (CDMG) with different water contents was studied using scanning electron microscopy, and its mineral composition distribution was obtained through X-ray powder diffraction. The results show that the mineral compositions of CDMG are mainly quartz, feldspar, montmorillonite, illite and kaolinite, with the average content of quartz and feldspar being 28.09% and 44.26% respectively. In the clay minerals, montmorillonite with strong hydrophilicity accounts for the highest proportion of 19.79%. The microstructure of the sample is composed of coarse-grained quartz and feldspar as the skeleton, and laminated and crushed clay minerals as the filling material to form a dense skeleton-filling structure. Through the statistical analysis of the particle morphology and pore distribution data of the sample, it is found that with the increase of moisture content, the content of fine sand keeps increasing and the arrangement of particles tends to be chaotic. The pore content and transfixion rate increased, and the content of the macropore increased significantly. The original filling structure was destroyed and the degree of compactness was greatly reduced due to the expansion potential induced by water absorption of hydrophilic clay minerals.