EMPLOYEE WAS WORKING ON 6 NORTH MAINS SECTION - IN PROCESS OF CUTTING OVERCAST - EMPLOYEE WAS HANDING AN 8 FT BOLT TO ROOF BOLTER OPERATOR - INSTALLING BOLT IN SCREEN - A PIECE OF ROCK FELL FROM ARCH - MEASURED 4 FT LONG X 2 FT WIDE X 3 INCHES TO 0 IN THICKNESS. STRUCK EMPLOYEE'S RIGHT HAND JUST BEHIND KNUCKLES - RESTING ON RIB PROTECTOR - AMPUTATION OF RIGHT RING FINGER.