Is this a grinding stone?

[simbad42]

my friends and I were talking it over once again and some say Mother Nature made this hole in this rock and some say it’s a old Native American rock? What’s your guys opinion?

 

[old digger]

Looks like a naturally eroded rock.

 

[Treasure_Hunter]

Don't see any signs on it to suggest used by man.

 

[quito]

This is an omarolluk, a natural piece similar to yours.

This one has been utilized, the rim as well as the bottom of the hole are nicely polished.

A pair of my grandkids mootched this off a neighbor of theirs.