Georgian/Victorian Pin?

Usually I prefer big and flashy costume jewelry over the smaller ones. This pin, however, caught my eye and I bought it even though it was neither large nor in perfect condition.
When I took it home and had a second good look at it I realized that I was a bit different from what I thought is was. The rectangular glass is actually a stone, possibly some kind of agate, and the pin itself seems to be a lot older than I originally imagined.
After searching in my books and on line, I found only similar looking pins from the Georgian and early Victorian era. For that reason I think that my pin is also very old.
I believe that the metal is rolled gold. I would appreciate any ideas from my fellow CW members.

Thanks for looking:)