Its hard to tell without signs of workings or wear marks,but WNCsweeper is right--they used anything in nature to achieve a task. Early Native Amer. didnt really have a need for a handle with crude era tools,most hand tools were rounded or small,to fit in hand easier,to do small tasks, big heavy non-specific rock tools were not easy to carry,something like that would have been used at the time time of need and discarded.--so stone age tool prob not--picked up and used by a native to crack a nut apart for a dinner around a fire -why not?