This is a unique 15 karat gold bar pin, 2 & 3/4 inches (bar) & 1 & 1/4 by 3/4 inches (opal), from the Edwardian era with a little chunk of the rainbow attached. The specimen is a boulder opal of incredible natural color. I love this setting because these were the days before doublets and triplets, so the matrix and gem layer are fully exposed. Today it would probably be bezel set to protect the stone (which is not much harder than glass) and people wouldn't believe it is a real stone. :) Opals are fragile complex combinations of silica and water. All the color you see is a trick of the light on the stones molecules. It is in excellent condition.