If you can get access to the river that runs through Fort Benning, outside Columbus, there is small material there, and maybe even a real gem or two. I never collected there, but we used to toss a keg off the top of a cliff, and then bury it in a gravel bar near a cold spring a short distance downstream. There was even an Indian shower as you climbed back up the edge of the cliff, headed for your car.
Excuse me! I was much younger then! Where I was going used to get you run off by the MP's, since they used that area as a single survival training area. Today, you might have homeland security looking at your tonsils if you went there!
I don't really know about the stone in the area other than that.