I would assume that it's a made-for-jewellery imitation. THe reverse has a big sun-star, nice and centred, for carefully soldering on a central mount to turn it into a button or cufflink. Given the big grey blob of removed solder in the middle of the reverse, I'd say this did indeed happen to this piece at one stage. Or, you can do what a prevous owner of this peice has done, and just drill your own hole.
It will likely date from after 1876, but probably not too long after - the style of lettering looks late 19th - early 20th century.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis