EE WAS BOLTING ON THE INTAKE SIDE OF THE RETURN BOLTER IN UNIT#1. EE WAS INSTALLING HIS 2ND BOLT IN THE 1ST ROW OF CUT IN #1 ENTRY. EE STATED THAT A PIECE OF ROCK BROKE LOOSE OVER HIS CANOPY & ROCK FELL VERTICALLY OFF THE EDGE OF HIS CANOPY AND STRUCK HIM ON RIGHT COLLARBONE. EE HAD SWELLING & TENDERNESS. ICE PACKS WERE APPLIED. ROCK WAS APPROX 8""X1""X2"" THICK.