In 23D at 39 block 2 to 1 (track chute) the employee was on the right side of the Joy 14ED25 miner installing the last strap in the entry (after holing). After finishing the drill hole, he lowered the timber jack and a piece of roof rock (18""x12""x1"") fell and struck his right elbow causing small lacerations and contusions. No issue with mining methods, compliance, PPE or training.