18ct White Gold Blue John Cushion 0.51 Carat Diamond Necklace. P2667. This elegant pendant boasts a stunning cabochon cushion piece of rare Blue John stone that has been sourced directly from Treak Cliff Cavern in Castleton. The stone is placed within an exquisite 18ct white gold setting and surrounded by glistening 0.51 carat brilliant cut diamonds, giving the piece a sophisticated sparkle. The pendant hangs from a fluid 18 inch long 18ct white gold chain. All our Blue John jewellery is designed and crafted within our very own workshops in Ashbourne, Derbyshire where a team of skilled craftsmen turn the raw Blue John stone into these stunning pieces of jewellery. You can find other matching Blue John jewellery and other Blue John necklaces on our website. 18ct White Gold Blue John Cushion 0.51 Carat Diamond Necklace. 18 inch long 18ct white gold chain (92097).