you can't judge a book by its cover, and it's the same with gems which include organic gems, which are softer on the Mohs Scale, like amber, conch shell (used for cameo carving) and pearls.
You can't evaluate the gem's worth by the covering of metal that's encasing them. It can influence but the hardware is not diagnostic of the software, if you get what I mean.
It makes identification of the material that much easier, for example, black opal, if the design is opened backed, but it could be encased in metal simply for protection, or because it was fashionable at that time, not necessarily just to hide evidence of an inferior, substitute or impostor gem.
Your earrings should be examined by a professional with expertise in the area of cameo jewelry.
