Discovered almost two thousand years ago by the Romans, Blue-John is a rare natural variety of Calcium Fluorite, highly distinctive and prized because of its characteristic bands of coloured veins. The only known deposit of this unusual mineral occurs in the hills to the west of Castleton, Hope Valley, Derbyshire, England, opposite the mountain known as 'Mam Tor', the shivering mountain.
The principal colours are purple and white, disposed in undulating bands and usually separated by a third band, the two colours being mixed, assuming a flame-like appearance.
Blue-John became increasingly popular in Britain in the late 18th- early 19th century. Mathew Boulton, probably the best English bronzier, extensively combined Blue-John with gilt-bronze mounts, in order to create Neo-Classical urns and candelabra.
The mines are now largely extinct.