Cabochon Opal & Diamond Pendant in 18k Yellow GoldCabochon Opal Diamond Pendant in 18k Yellow Gold. This fantastic opal and diamond pendant features a 1. 17 carat cabochon cut opal that is prong set in 18 karat yellow gold and wrapped in a halo of round brilliant diamonds. The thin 18 inch gold chain features dainty little diamonds spaced evenly and providing a bit of movement and sparkle. This would be an amazing necklace for everyday wear and would look fabulous with a group of other chains.