how old is my shell cameo brooch and how much is it worth?

I received a a shell cameo brooch which has the profile of 2 people on it. A man's face profile in the background and the other is a woman's face profile. I had the metal tested and it is solid 14kt gold. It has a "c" clasp (hook) for the pin. I haven't seen many of these with two profiles. Does that mean anything? How old do you think it is and how much would you estimate it to be? Thanks