Crack initiation and propagation are key scientific questions influencing rock failure. To study crack initiation and propagation during rock failure, CT scanning tests were performed on the sandstone samples. The initiation and propagation stages of sandstone cracks were analysed based on a reconstructed three-dimensional crack structure model. The types of crack initiation and propagation in minerals and the effects of mineral composition heterogeneity on crack initiation and propagation were studied using microscopic analytical techniques. The effect of mineral granularity on crack initiation and propagation was analysed using statistical methods. The results show that crack initiation and propagation can be divided into four stages: microcrack inoculation, mesocrack initiation, mesocrack evolution to macrocrack, and macrocrack penetration. Four cracks are formed at different locations, extending along the mineral edge, deflecting at the mineral edge, bifurcating at the mineral edge, and penetrating through the mineral. The poikilitic texture formed by quartz debris and cement makes it easy for cracks to extend along the mineral edges. In quartz debris with high crystallinity, the crack tends to deflect and bifurcate at the edge of quartz debris. The symbiotic structure of altered quartz and clay minerals easily causes cracks to propagate through the minerals. Furthermore, the distribution of mineral granularity affects crack initiation and propagation. The inhomogeneity of mineral granularity can easily cause the initiation and propagation of cracks. The size of the mineral granularity affects the width of the secondary crack. These research results can provide a basis and reference for predicting and evaluating the stability of rock masses.

裂纹萌生和扩展是影响岩石破坏的关键科学问题。为了研究岩石破坏过程中裂纹的萌生和扩展，对砂岩样品进行了 CT 扫描测试。基于重建的三维裂缝结构模型分析了砂岩裂缝的萌生和扩展阶段。利用显微分析技术研究了矿物中裂纹萌生和扩展的类型以及矿物成分不均匀性对裂纹萌生和扩展的影响。使用统计方法分析了矿物粒度对裂纹萌生和扩展的影响。结果表明，裂纹的萌生和扩展可分为微裂纹孕育、细观裂纹萌生、细观裂纹向宏观裂纹演化和宏观裂纹渗透四个阶段。在不同位置形成4条裂缝，沿矿缘延伸，在矿缘处偏转，在矿缘处分叉，并贯穿矿物。由石英碎屑和胶结物形成的晶质岩结构使得裂纹很容易沿着矿物边缘延伸。在结晶度高的石英碎屑中，裂纹往往在石英碎屑的边缘发生偏斜和分叉。蚀变石英和粘土矿物的共生结构很容易导致裂缝在矿物中扩展。此外，矿物粒度的分布影响裂纹的萌生和扩展。矿物粒度的不均匀性易引起裂纹的萌生和扩展。矿物粒度的大小影响二次裂纹的宽度。