18ct white gold blue john 025ct brilliant cut diamond oval ring r900 this enchanting ring boasts an unmissable oval shaped piece of rare blue john stone in the centre that has been directly sourced from treak cliff cavern in castleton the stone is set within exquisite 18 carat white gold and surrounded by mesmerising 025 carat brilliant cut diamonds that run down the shoulders of the classic band all our blue john jewellery is designed and crafted within our very own workshops in ashbourne