Silver blue john marcasite cushion ring r745 this simple and stylish ring boasts a delicate cabochon square shaped piece of rare blue john stone in the centre that has been sourced directly from the derbyshire blue john cavern in castleton the stone is placed within an elegant sterling silver square setting embellished by dazzling marcasite stones for an unmissable sparkle the ring is complete by a classic sterling silver band all our blue john jewellery is designed and crafted within our v