If that is what I think it is, it's ancient glass (not just old or antique) It could be Roman. And it could be more modern Art Nouveau If it is a repro they did a good job making the glass look like it was in advanced stages of decomposition.
I'd say you need a roman or ancient Persian glass expert to evaluate that. it's either a really decent piece of ancient glass or a very good fake. Not my area. For a garage sale find it's got a lot of potential.