The injured was installing the last bolt of the cut.The EE let the drill mast down to retrieve the wrench out of the drillpot with his right hand, when he got a hold of the wrench a rock fell from top and caught his little finger between the rock and the wrench. The rock meas. 20"" X 20"" and 1/4 to 4"" thick. Right little finger was amputated just behind his finger nail.