Hm. From the picture it looks dodgy to me... but the picture might also be dodgy... the color behind and under the ring makes me nervous, but it's hard to say. Plenty of counterfeits exist for these types of coins. It would also have to be a half or quarter noble at that size. Full nobles are somewhat larger. Anyway, it's pretty difficult to make out any details with those photos. Plus, as already asked above, what does the other side look like?
As already stated there's no way to say based on those pics. My guess is it was part of a charm bracelet at one time, and if it was it could be genuine or a modern copy with both being equally likely. But even if we were to assume that it was genuine, given its condition, holed and obviously very polished, it would have little value as a collectible.
