Yes, that's a very nice and large vug for that Savannah River material.
And, as Rebecca and John have already said, a real pretty
blue on the botryoidal chalcedony druse.
I would first have to look closer, with a loupe, at all the
dark spots to make sure they are just dirt before washing
them away. Then take a wet toothbrush and try a little area
before going at the whole piece. There can be a lot of
interesting accessory minerals found in those vugs.
Toward the bottom of this link they have a list of some of
the accessory minerals you can find. (Even tho I think they
have mis-spelled chalcedony in their list.
)
http://www.aikengmfs.org/PowerPoints/2012AGMF_Girard_Chert.pdf
Thanks for the pic,
Joe