Cushion Cut Aquamarine Cocktail Ring in White GoldCushion Cut Aquamarine Cocktail Ring in White Gold. This extraordinary GIA certified natural aquamarine is truly the most desirable color. Known as a Santa Maria aquamarine this fine 9. 20 carat cushion cut gemstone is a rich sky blue with a grey undertone. The custom 18 karat white gold setting feature channel set baguette cut diamonds set into the basket and further accented with round brilliant diamonds just before the high polish shank.