Found on Nantucket doing some searching near the harbor...near the other hammerstone I found. I'm not 100% on this one. The context is right and it certainly shows wear on a couple of the sides.
It could be but when you find a round rock you have to think would this one hold up as a Hammerstone by hitting another rock. To me the material looks like something that might crack in half with a good hard wack. I dont think its a grinder either due to there is no smooth areas that I can see. jmo
Thanks rock. I actually whacked it a bunch of times when I first grabbed it because I thought the same thing. It crushed the cobble and showed almost no damage. When I get home I'll try for a close up hi-res picture.