Back in the 1970's my dad found this in Balmoreah, TX. He was an avid arrowhead hunter and made a rock garden. I guess I just want to know for sure that it is a concretion and nothing else. It's very large at 10 1/2" x 6" and heavy yet porous (at least on the surface.). Also, he was at one time told that the Indians used these for rolling on hides.