Found this stone object on private property near 2 known prehistoric settlements: a Middle Woodland site (Candy Creek), and a Mississippian (Ledford Island) along Tennessee's Hiwassee River.
If it was used as a hammer, I would expect to see battering evidence on the business end. From your pics, I'd say it is a naturally formed stone. Keep looking though. There's a lot more artifacts in the ground to be found. Good luck.