Thought this was brass or gold plated but it just cleaned up too good. Looking for a hallmark but I don't see one. I'm thinking it's 9 or 10K. There was no picture inside when I opened it up.
Nice find, lockets are always interesting! The hallmark or quality stamp is often on the attachment ring that held the locket to a chain or whatever and it is missing. The only way to know for sure is to have it tested. HH, Mike