Friend of mine brought this by, said he found it down in Bimini (Bahamas). I can't find a date or denomination, but I can read the ruler as Franz Joseph / Austria / Imperator. Item is about the size of a dime and is heavily worn (most likely due to sand.)
It's the size of a dime (so not a florin) and the stars around the reverse (which you can't really tell from my cell phone photo, unfortunately - just around 5 pm) should be text (at least on every other example I could find in the Krause.) It would be great if I could see a date, or a denomination...but that side is so worn I'm not sure I'll be able to attribute it without someone saying, "I've seen that before."
I'm not familiar with this, but first impression leaves me feeling like it was a cast for jewelry. It must have some value as the chain has worm most of the post away, so I think someone wore it for a long time.