Any ID on this incredibly strange looking rock formation

[Gregg3131]

Found this on a river bank near an old Native American cave. The indentations seem almost symmetrical. It may be limestone? ? I have no idea on this one. Object is about 7inches or so.

 

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[DannyB1954]

Maybe used to start fires? Spin a stick between a rock and a piece of something that will burn. How to Start a Fire with Sticks (with Pictures) - wikiHow
Just a thought.

 

[Gold Maven]

looks more like a fossil to me,

 

[DannyB1954]

Maybe also ask in the North American Indian Artifact area. It looks like a wear pattern to me. One area gets too deep, they start another spot.
I have seen larger rocks worn like this where Native Americans have ground up acorns.

 

[Simon1]

Primitive form of brass knuckles ?
I have seen something like that before myself many ions ago and along a river bank. Mine was in the central part of the U.S. though.

 

[Simon1]

If memory serves me, what I had found was maybe 4 or 5 " long, again, many ,many, many years ago. I might still possibly have it out in the garage. Very similar, and in very different parts of the country, only having a riverbank as common denominator.

 

[Gregg3131]

Any idea of how old it was and what purpose was? Everyone is all over the board on this from natural water wear to fossil etc. To me it just seems to symmetrical to be natural. Even under the hole indentations seem to be other finger nail like marks all in a row....but I am far from a rock formations expert.

 

[Bajahunter]

Looks like some kind of fossil coral to me.
It looks natural to me, not made by man.

 

[ice9]

Very interesting. It's hard to tell, but I do not think it's fossilized coral. See what a local archaeologist or Indian expert in your area can tell you.

 

[DCMetal]

Paint bowl stone?