Blue John Fluorite Mineral Specimen United Kingdom 400g 15

£99.99

Blue John specimen 400g and measuring 105:71:41mm. Blue John (also known as Derbyshire Spar) is a semi-precious mineral, a rare form of fluorite with bands of a purple-blue or yellowish colour. In the United Kingdom it is found only at Blue John Cavern and Treak Cliff Cavern at Castleton in Derbyshire. During the 19th century, it was mined for its ornamental value, and mining continues on a small scale. The most common explanation for the name is that it derives from the French bleu-jaune, meaning 'blue-yellow'. The story goes that Blue John was exported to France where it was used by ormolu workers during the reign of Louis XVI (1774–92). However, there is no archival record of any Blue John being exported to France,[1]:?7? and the early ormolu ornaments which use Blue John were being manufactured by Matthew Boulton of Birmingham in the 1760s. In the United Kingdom, the blue, banded fluorite known as Blue John is found only under the triangular hill known as Treak Cliff, just outside the village of Castleton.[1]:?20? Today the veins are mined only in Blue John Cavern and the nearby Treak Cliff Cavern, although the abandoned Old Tor Mine on the north side of Winnats Pass was also, at one time, a source for the mineral.