EE AND COWORKER WERE ROOF BOLTING A FRESH CUT. THEY WERE ON THEIR THIRD ROLL OF INSTALLATION. WHILE EE'S STEEL WAS BEING SET UP FOR DRILLING HOLE A PIECE OF BLACK SLATE APPROX 3'X 2'X 6"" THICK FELL AT POINT OF CONTACT WITH DRILL STEEL, FELL ONTO EE'S RT SIDE OF NECK CAUSING LACERATION TO RT SIDE OF NECK WHICH REQUIRED 11 STITCHES.