A beautiful cabochon opal of quite sensation colour having strong green and minor orange and indigo play of colour over a white base.  The opal measures approx. 18.8mm x 14.8mm x 4.8mm deep and is claw set into a open work  yellow and white mount attaching via a small gold ring to a  yellow rectangular necklace loop.  No hallmarked, stamped 750 and testing as 18ct yellow and white gold