A Nanoindentation-Based Study on the Mechanical Properties of Main Rock-Forming Minerals in Granite

Granite is widely used in buildings, stone carvings, and sculptures, where long-term durability is strongly influenced by the micromechanical behavior of its constituent minerals and mineral interfaces. However, conventional rock mechanics tests cannot resolve the mechanical heterogeneity at the mineral scale, particularly at mineral interfaces. To address this limitation, a systematic nanoindentation study was conducted to quantitatively characterize the elastic modulus, hardness, creep behavior, residual deformation, and fracture toughness of both individual minerals and mineral interfaces in granite, and to clarify their mechanical contrasts and interrelationships. The results show that the constituent minerals quartz, feldspar, and biotite exhibit elastic modulus of 121.9 GPa, 115.6 GPa, and 66.3 GPa, respectively. Quartz and feldspar show relatively better mechanical properties, whereas biotite exhibits the weakest mechanical behavior. Hardness shows the same trend. In contrast, creep displacement and residual indentation depth follow the opposite order, i.e., quartz < feldspar < biotite. In addition, the elastic modulus and hardness of mineral interfaces are lower than those of the adjacent minerals, whereas their creep displacement and residual indentation depth are higher. The dispersion of these micromechanical parameters for mineral interfaces is generally greater than that of the adjacent minerals. The fracture toughness values of both minerals and mineral interfaces were also obtained: mineral fracture toughness ranges from 3.1 to 6.2 MPa·m0.5, while mineral interfaces range from 0.7 to 4.3 MPa·m0.5. Further analysis of the micromechanical parameters indicates that elastic modulus, hardness, and fracture toughness exhibit clear positive correlations among minerals, mineral interfaces, and the mineral aggregate. Comparatively, the correlations are strongest for minerals and weakest for mineral interfaces.