CAMEOS  not a birthstone, nor an anniversary stone.  

A stone or shell cut in relief using the object itself to produce shadings of the carving from the Hebrew word kamea----a charm or amulet or Latin cammaeus "engraved gem". These are said to be the root origin of the word CAMEO, but even among experts even this is disputed. 

There are two different methods of carvings of a cameo: 
1. Relief---carved from the front with only the front profile showing or one side as opposed to a sculpture that can be seen from all sides. 
2. Intaglio----carved from the rear of the profile or picture. 

Just when the first cameo was carved is unknown and shrouded in mystery, but we do believe it was in Greece or Rome. Cameos were quite popular in both areas and were carved from stone such as AGATE. Shell was not used until a much later date. Because of their availability and the ease in which they could be carved, shells became extremely popular and eventually the art of cameo carving settled in a small town, Torre Del Greco, at the base of Mt. Vesuvius, located on the Bay of Naples. The tiny town of Torre Del Greco, Italy, today, is still the center of Cameo carving. Over 25 different sea shells are used plus a large array of coral. Most shells originate in the Bahamas, the West Indies, and Madagascar. 

(There is lots of information around about cameos this is only a shorten version to give you a bit for more.)