Matt is probably right that it's a Civil War era token, but I can't find the exact one on eBay or with a Google image search. The neck is the issue. Can't find any coin with a neck like that one.
I did give it 10 minutes in hydrogen peroxide, but that only made it worse. Not much detail left on the reverse anyway. Found it in a spot that's wet most of the year. Every coin I've found in this area has been toasted.
I'll keep looking, but it may be a lost cause. Could be a local token with a small mintage. It's a heavy coin and seems to be a quality piece, but 150 years in the ground has taken it's toll...