coosakid, your piece is definitely naturally formed and not an artifact of any kind. And in my opinion, what jmaschal posted above are all natural concretions with the exception of the piece with the Pestle setting in it. Everyone calls those "Paint Pots" or "Firestarters" when in fact they are most likely neither. I have a spot along the Ohio River where I can fill my pockets with the Concretions pictured in his post. None are artifacts or "Paint Pots".