Silver Blue John Marcasite Square Ring. R751. This stunning ring boasts a delicate square shaped cabochon of rare Blue John stone that has been sourced directly from the Treak Cliff Cavern in Castleton. The stone is placed within an exquisite sterling silver setting embellished by dazzling marcasite stones, bringing a sophisticated sparkle to the piece. The ring is completed by a classic sterling silver band. 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 rings on our website. Silver Blue John Marcasite Square Ring. Ring measures 12x12mm at widest point. Blue John measures 4x4mm.