Not sure if this link will help. I know we found all types of rocks in paulding county.
Geology of Georgia
I don't know the right terms..I think they were called thermal vents?Volcanic tubes? Where different rocks or minerals show up in one place. So, your rock could possibly be volcanic, or slag dumped years ago off the side of a hill as fill. I don't know enough to Identify it. I'm still new to the Geology stuff. GA has a variety of stuff! Not being from here, when we moved here it was a whole new world of rocks and cool stuff! Our neighbors watch and laugh when we're on our hands and knees in the yard looking at the new stuff that washed out of a hill, and putting it in our pockets!