old cameo locket with pearls

Hello, I'm new to antiquing and have amassed quite a motley assortment which I plan to eventually sell. I'm really struggling with dating a few pieces. This locket looks to be bronze with a black cameo (I don't know the material but would love to) surrounded by what looks to be tiny pearls. There are no markings on it giving any information about it. I'd love to gain enough into that I can talk about this piece and the materials it's made from and properly price it. I'd REALLY like to know an estimate on the year it was made.

Any help is so greatly appreciated. I know it's hard to properly give advice when you can't see it in person so hopefully I have a good description. 

THANK YOU!!

Fair