EE was performing his preshift exam He found some loose rock located in the crosscut between No.3 & No.4 entry that needed to be taken down. After scaling down the rock, he turned to walk away when a piece of rock approx 3'x2.5'x3.5"" fell out striking him on the back of his right leg. He finished his shift then report it. The rock caused a small fracture in his leg.