3 Carat Oval Sapphire & Diamond Ring in Platinum3 Carat Oval Sapphire Diamond Ring in Platinum. This dazzling ring features 1. 37 carats of diamonds and a wonderful 3. 12 carat oval cut sapphire and is finished in platinum. The sapphire is prong set and surrounded by a halo of round cut diamonds with an emerald cut diamond on each side where the shoulders meet the center stone. The prongs on the outer edge of the accent diamonds create points that evoke the icy look of a unique winter snowflake.