2.18 Sapphire Diamond Engagement Ring in 18k Platinum. This Mid-Century three stone engagement ring features .90 carats of Round Brilliant cut diamonds and a 2.18 carat cushion cut  blue sapphire finished in platinum and 18K yellow gold. Two (2) .45 carat diamonds sparkle against the cushion cut center sapphire. Set in platinum prongs, the blue sapphire has a radiant, royal blue hue. From the profile, vintage crown baskets support the gems, finished on a polished 18K yellow gold band.