These come into my local artifact shows frequently. And they are actually concretions. They are a harder, denser, 'ball' of sediment that form with softer material and when the erode out and get moved around, they can give the appearance of being something that man would have utilized. When i started collecting at around age 13, i had some that i thought were axes... But then i learned about them. Always pick everything up and question it though, cuz you never know!