Black Opal Dual Ring | Size OA distinct and elegant 3. 30ct Lightning Ridge black Opal ring. With swirling, glowing greens and an undertone of turquoise blue. Set in a proud bezel and fused dual ring made from Argentium Silver, which is hypoallergenic, tarnish resistant, purer than sterling silver and brighter in colour. Ready to ship in UK ring size O and hallmarked by The London Assay Office. Please get in touch if you'd like to see a short video of this ring in action.