That is Silverfish Stone from vanilla Minecraft which only generates in Extreme Hills.
That makes a lot of sense.
Also in the default configs is there any way to actually obtain amercium, europium, neutronium, and whatever other exotic end game materials that may exist?
nvm I found it. Herpin' everywhere today.
Actually on that note: I noticed that even without optifine the fusion reactor gui has an NEI button but the mouseover highlight is shifted to the left a bit and you can't click on it to see the recipes. I had to go to the wiki. Is this intentional?
I'm on GT 5.08.19, NEI 22.214.171.124, and forge 1420