Employee was standing 18' back from start of XC 7L on unit 5. A piece of slate 5'Lx32""Wx3""T fell from between the rib pins and the rib and struck his head, rt arm and thigh. There were no spread pins and all had pie pans. He was taken to the ER and diagnosed with contusions, no stitches or fractures. He was unable to work his next scheduled shift.