A friend and I have been hunting a plowed field. I have yet to find a point, but he found 2. In the same area of the field, I located this broken piece. It feels like an exceptionally heavy/dense material. 2 parallel sides are smooth, while the other set of parallel sides are the same roughness as the break. It appears that the two smooth sides have been deliberately worked down. Also, there is some sort of divot in the end. The line crossing the divot is a vein of mineral or quarts or something and it continues down one of the rough sides.
Like the others said probably used for grinding grain but broken. The are usually round and flat on the one. They are call a pestle. Not sure why it has a flat side however. I've never seen a pestle like that. So I'm not 100% sure that's what it is.