The Lone Survivor

This Cameo has been in my family for generations. My Mom gave it to me over twenty years ago and I thought it was lost at least ten years ago. Last year, when I moved, all my gold jewlery was stolen. I was doing some in depth cleaning out of my "memory" boxes, when this piece came up out of nowhere! now it is the only Heirloom I have left. how do I find the monetary value on a piece like this?