Crystallographic constraints on microcrack dynamics in granite: Insights from in-situ microscopic characterization of crack network propagation

Accurate prediction of crack behavior in granite is essential for advancing geological engineering, geothermal energy extraction, and nuclear waste disposal. However, the microcrack dynamics governing fracture initiation and propagation remain poorly understood due to the complex interplay between mineral heterogeneity and local stress fields. Here, we reveal the fundamental mechanisms of microcrack evolution in granite at the mineral texture scale through in situ scanning electron microscopy (SEM) observations under shear and tensile loading. By integrating energy dispersive spectroscopy (EDS), backscattered electron (BSE) imaging, and electron backscatter diffraction (EBSD), we uncover how microstructural features—such as mineral boundaries, grain defects, and crystallographic orientation differences—control crack initiation and growth paths. Our results demonstrate that local stress field disturbances lead to crack branching, deflection, and en-echelon formations, with intergranular and transgranular fracture modes dictated by grain-scale heterogeneities. These findings provide a mechanistic framework for understanding fracture propagation in crystalline rocks, offering critical insights for refining rock mechanics models and designing stable geological structures in energy and environmental applications.