18K White Gold Cushion Cut Blue Sapphire Diamond Halo Engagement RingA gorgeous cushion cut, 7. 48 carat, heat treated blue sapphire is the focus of this magnificent piece, accented by a yellow gold prong setting. Set into 18K white gold, it is surrounded with a round diamond halo and flanked by two half round cut diamonds, one on either side. It's finished off with a quarter eternity band set with round diamonds.