Drilling and blasting is one of the most convenient and commonly used methods to break rocks in mining and civil applications. Due to numerous environmental, safety and productivity issues, the industry and contractors are looking for an alternative rock breaking system. Heating of rocks and minerals with the help of microwave treatments has therefore been the topic of many laboratory investigations and field tests since last decades. The focus of this research is to describe the effect of microwave energy on big samples of hard Granite rocks which are not completely wave absorbent. 3 different tests were carried out using high power density radiation with magnitudes of 15 KW and 20 KW on 3 Granite blocks at Sandvik Company with the help of a 30 KW industrial microwave machine. Further on, after drilling and preparing the core and getting Computer tomography images, a complete sketch of all the cracks in small-scale and big-scale conditions were digitally made using AutoCAD software. It was concluded that microwave energy generates high temperatures within the rocks and causes a small thermal damage on the surface that leads to a crack network underneath. By means of this investigation, it is also believed that heating is not a source directly for crack itself, but it is an initiation for thermal fracturing and later cracking