Admittedly, I'm not certain of what this brooch is made up of; I do know it is not bakelite and I really don't want to put a hot needle to it to test for plastic or amber.  I did research amber and it certainly has all the characteristics of a baltic amber.  It is marked on the back with a backwards R and KG.  Possibly a Russian mark?  If anyone knows, I'd appreciate it if you could share the information.

This brooch looks somewhat like a snail shell; it measures 1 1/2" x 1 1/16" and is set on a gold tone (maybe real) setting.  It is carved along one side.  It is in very good condition.