greenacres, the better name would be "native American axe" given it was found in NJ.
It could be anywhere from 1,000 to 13,000+ years old.
HA, if it was pre-historic ....... then it wouldn't exist.
They really can't "date" stone or flint, they assign a date to it depending on it's "shape" and/or where it was found. See link below:
Grooved, Ground Stone Axehead,
Eastern Woodlands cultures, Woodland Period (800 BCE-1000 CE), Stone (Granite?),
http://art.missouristate.edu/arthist/exhibit1.php?E=1&P=36