You never know what you're going to find, but a stone tool usually is chipped or damaged where the striking edge is located..This is prominent on axes and celts....Most tools also display "pecking", a process where the tool maker formed a certain tool from rock, using a piece of antler or another harder rock..Pecking will appear as a rash of little pin pricks, similar to using an ice-pick on something to chip away material...In this case I'm inclined to believe that this may simply be a rock, but put it on Ebay as a tool, and someone will buy it!