Blue John Oblong Marcasite Silver Bracelet. B878. This simple but stunning bracelet boasts a small oblong shaped piece of Blue John stone that has been sourced directly from Treak Cliff Cavern in Castleton. The Blue John stone is set on a delicate sterling silver square linked chain that is embellished with exquisite marcasite stone for a sparkly finish. 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 bracelets on our website. Sterling Silver and Blue John.