Years ago my father had a place on a small tributary of the Mullica River just north of Atlantic City. He had a large smooth stone shaped like a large Idaho potato, which he used as a door stop, and in the winter to heat in the oven and warm the foot of the bed. Now I wonder if it could have been an Indian grinding stone. It was about 8 inches long with an oval center about 2 inches by 3 inches. I know NJ had Indians living in that area.
Yes. That is a grinder. I have one somewhere in the basement, possibly Archaic period for Maryland, about 1,000-2,000 BC. Indians seemed to use that basic design for grinding because you could hold the stone in the middle and you had two grinding heads. They should show up a lot in the periods/tribes in No. America and Latin America who ate maize/corn and grain foods (wheat, rye, etc).
Try looking them up on the internet, possibly using a search term “Indian corn grinder”, “Indian pestol/pestal” (pestal and matatae something like that), “Indian food masher”, etc.
Sometimes they might have also been used as smashing axe-heads or even as small plowing stones.
If the stone your father found was north of Atlantic City, it probably came from the “Gilante or Gigante Tribe”, a member of the “Gambino/Patriarcha Confederation of Italian Indians”. /sarc
I could also have been postcolumbian, ftm.