I think it is a natural rock and not a native made relic but very well could have been used by a native as a net weight, huge bead or...... It's a cool piece and I would have brought it home. Good Find.
A very interesting rock, but I agree with "Indian Steve" that it's a natural formation. Notice the different shades of color orbiting out from the eroded hole, they are indicative of a different density within the stone. The soft middle has eroded away by natural causes. Lots of stone like that down around Waco and other places.