Blue John Necklace Owl With Marcasite Eyes. P2322. Set within the eyes and belly of this cute and quirky owl pendant are three stunning round pieces of rare Blue John stone that has been sourced directly from Treak Cliff Cavern in Castleton. The sterling silver owl design is further embellished by glistening marcasite set around the Blue John in the eyes, giving the piece a touch of sophisticated sparkle. The pendant hangs gracefully off a delicate sterling silver chain complete with a classic bolt ring clasp. 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. Sterling Silver and Blue John.