Observation of microcracks in granite using a confocal laser scanning microscope

Microcrack generation and propagation of coarse- and fine-grained granites were investigated under a confocal laser scanning microscope (CLSM) observation. The microphotographs were obtained for different stages of the applied stresses corresponding to the different cracking zones as mentioned in the stress strain relationship of granite. The microphotographs under CLSM showed that the microcracks were initiated from the crack tips where the maximum stress concentration may occur while in previous studies under light microscope (LM) or stereoscopic microscope it was found that the microcracks initiate from the grain boundary. Results revealed that the microcracks were propagated first perpendicular to the loading direction towards the weak crystalline surface of the feldspar and then parallel to the loading direction towards the quartz. Microcracks were also initiated from the corner tips of biotite and then propagated towards the weak crystalline surface of feldspar and then parallel to the loading direction. The microcracks in the fine grain granite were initiated at a later stage of applied stress than the coarse one because it has a numerous number of contacts between the grains offering the high bondage of cementing material. Thus the CLSM observation described in this paper may be considered as an improved method of analyzing microcracks in rocks.