The brooch is pre-1930s. See how long the actual pin is, as old brooches have a much longer pin than modern ones. As you can see, the pin goes over the brooch edge. It's a very old setting.
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Cameo Found by: Anonymous
What a wonderful find! Cameo's are highly sought after by collectors. The more precious the materials the more valuable. Many things come into play such portrait displayed on the cameo. I would start by looking for purity markings such as "14k" on your piece, though if it is an early cameo, it may not be marked. A real cameo will always be carved from one single stone, imitations will be glued or fixed onto the piece. Good luck! :)