Silver Blue John Marcasite Triangle Ring. R820. This elegant ring boasts a striking marquise shaped cabochon of rare Blue John stone that has been directly sourced from Treak Cliff Cavern in Castleton. The stone is placed within an exquisite sterling silver diamond setting that has been embellished by dazzling marcasite stones which bring 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 Triangle Ring. 29x16mm.