Garnet Pendant?

This is another item I received from my grandmother. The little stone seems to be a garnet, but I am not sure. The pendant is not marked and I am almost certain that it is not gold. My grandmother always said it was "double" - I am not sure how to spell it but my understanding is that it is meant to look like gold but is possibly an alloy.
Based on the design I believe it might be Edwardian. Any ideas?

Thanks for looking:)