Well, you know how it goes, hard to say without having them in hand. Looks like quartzite, which being very dense, has that "heavy" feel you describe. On both, the ends look battered in an unnatural way and both look to be about the right size to be good for crushing up seeds or shelling acorns and hickory nuts, so I think it's possible you have something there. Not flint knapping hammer stones, though. I busted up a bunch of hickory nuts once to make hickory nut soup and I used a piece of quartzite like that.