This is definitely going to be one for JoeM's knowledge. I think it is some kind of Limestone on the outside, like a crust, that varies in thickness from a fraction of inch to a couple inches. A nail wont scratch the smooth gray but will the outside crust. White Quartz rock will scratch all it. It fractures conchoidal and the flakes are scalpel sharp but very brittle.
I can take more pics if it will help identify.

Thank you so much for the identification JoeM!!! The 600 million yrs old made my wife want to inspect a hunk of it, lol. You also have me reading up on the Uwharrie Mountain Chain. Rhyolite didnt even cross my mind, I thought the whole rock was some sort of Limestone. I have a thick piece of the outer crust somewhere with small square Pyrite crystal. I found it on my property by accident. It looked like it was an ugly slab of cement broken into chunks. The bottom looks like it was poured into a mold in the clay. I have been knocking pieces off of pure white Quartz , (milky?), and calling it knapping but I have a lot to learn about reading and listening to the material. I doubt I'll ever produce anything like below but, I'm dang sure going to try.
If you want some of this Rhyolite, I'll be happy to share.

I have found a lot of artifacts made from all kinds of material but, white to clear Quartz is probably 90%. Yep, Marrow Mnt on left and the other I'm still trying to figure out. It's the only point I've found with the tiny ears. I believe I live on what was a seasonal camp or village because of the "may be" farming tools I've found in my food plots near the creek. I will be posting some in "Artifacts" for opinions.