As EE was installing roof bolt in #7 right on #1 unit, a piece of slip rock approx. 2 1/2"" long x 2 1/2"" wide x 2"" thick fell out from above the fly board & struck him on the face, neck & his lower bicep. He received a laceration to his neck & abrasions to his bicep & face. He left in an ambulance & returned to work his next shift. This is being reported as a medical incident.