Jeanne thank you for writing in with your question. Can you tell us please if the cameo is a brooch as you mentioned a gold surround? If it is a brooch the style of the closure will provide dating clues.
Try to see (you will need a hand lens or jeweler's loupe as the markings have probably worn over time). If you can find any marks or signatures on the cameo material this will provide dating clues and add to the value.
Probably the most important thing is to distinguish if the cameo is hand cut or ultrasonically cut, the later produces rapidly reproduced copies of the works of master cameo carvers which are less valuable than the hand cut originals. The ultrasonic cut produces an effect described as "freshly fallen snow" and this "frosted" appearance can be easily detected in the deep recesses of any cameo which has been produced by the ultrasonic method, even if it has been finished by hand.
Condition is another determining factor. Hairline cracks and fractures that may only be visible under loupe will also detract from the price.
The artistic value of the carving is an overriding factor . If you prefer to get an on-line appraisal carried out you would be required to submit clear images, as close-up as possible.
