Blue John. | Carlton Hobbs UK

February 5 2010, 1:09pm

First discovered over two thousand years ago by the Romans, Blue John is an unusual mineral from the area around Mam Tor mountain at Treak Cliff near Castleton in Derbyshire, England (figure 2). This is the only known location where Blue John can be found, though other types of fluorspars are mined throughout the world. The name “Blue John” is believed to derive from the French bleu jaune,1 meaning “blue-yellow,” and it is characterized by bands of blue/purple and yellow/white colored veins. It is a difficult material to work with, as the stone is soft, brittle, and can be altered in coloration by excessive heating.2 Because of its rarity, the material is no longer used on a grand scale. Presently, only approximately one quarter of a ton is excavated each year and is used primarily for jewelry and small objects.