Silver blue john twist centre edge marcasite ring r752 this feminine sterling silver blue john and marcasite ringfeatures an ovalcabochonof blue john stone that has been sourced directly from treak cliff cavern castleton derbyshire the striking stone issurrounded by glittering marcasite and framed by a beaded silver design all our blue johnjewellery is designed and crafted within our very own workshops in ashbourne derbyshire where a team of skilled craftsmen turn the raw blue jo