blue john

Originally discovered by the Romans, during the 19th century it was mined for its ornamental value, and mining continues on a small scale. This material is a rare form of the mineral fluorite and is only found commercially in one mine in the world - “Treak Cliff” Cavern, England. Mined by Adam's friend John, it featured on the BBC's One Show in 2014/15. It takes its name from the French “bleu & jaune” (blue & yellow) describing the colours it displays.