Silver Blue John Marcasite Butterfly Necklace. N992. This stunning butterfly necklace is handmade in sterling silver and features four beautifully hand carved Blue John gemstones, sourced directly from Treak Cliff Cavern in Castleton, which are surrounded in a silver frame accented with sparkling Marcasite gemstones. The necklace is completed with 45cm long sterling silver chain. It is an exquisite and detailed piece which would make a beautiful gift. All our Blue John jewellery is designed and crafted within our very own workshops in Derbyshire where a team of skilled craftsmen turn the raw Blue John into these stunning pieces of jewellery. You can find other matching Blue John jewellery on our website. Silver Blue John Marcasite Butterfly Necklace. 32x47mm. Length 45cm.