4.15 Oval Sapphire & Diamond Engagement Ring in 18k4. 15 Oval Sapphire Diamond Engagement Ring in 18k. This modern engagement ring features an absolutely dreamy oval cut 4. 15 carat sapphire with 1. 14 carats of diamond accents finished in 18 karat white gold. The blue sapphire has a deep, royal blue hue and is haloed by thirty eight (38) . 03 carat diamonds. From the profile, an ornate basket mounting holds the collection of stones. The setting is strong and elegant and will exude a luxurious style