Blue John stone: a remarkable fluorite from a limestone cavern
Blue John stone is the name given to banded fluorite found in the Castleton area of Derbyshire in England (Ollernshaw, 1964). It has been prized for centuries. Chemically, it is a calcium fluoride (CaF2) and occurs in distinct bands of different colours: blue, white, purple and yellow. The colour banding is thought to be from periodic changes in the composition of the mineralising solution and the physical conditions during its formation (Mackenzie and Green, 1971). The name of this distinctive material is thought to have come from the French “bleu et jaune”, referring to its blue and yellow colours.
Blue John is mined from only two places – Treak Cliff Cavern and Blue John Cavern in Castleton. It occurs either in veins up to 3 inches thick or as nodules in a limestone unit found inside natural caverns beneath a hill west of Castleton. The caverns are now tourist attractions, where visitors can go on underground tours (British Council, 2008).
Castleton is an excellent example of a quintessential English town. A beautiful stream quietly flows through this picturesque community of quaint tea shops, inviting pubs, charming cottages and old stone houses. Peveril Castle is a short walk up the hillside.
Blue John was first discovered about 2,000 years ago when the Romans mined lead and other ores in the caverns of Castleton. The Romans valued its beauty and mined it for use in ornamentation.
Two vases made of the stone were unearthed during archaeological excavations at Pompeii. Artefacts made of Blue John have been found at other ancient Roman sites and there are several references to the stone in Roman literature. It was also in demand in the 18th and 19th century for ornamental vases and columns used in some of the finest houses in Britain.
Today, the larger Blue John veins are largely mined out and the material is now scarce – only a few hundred pounds in weight are mined each year for specimens, ornamental pieces and for jewellery sold in shops in Castleton.
References
British Council, 2008. “Going down the mine.” British Council Web site: Retrieved March 21, 2009, from http://www.britishcouncil.org/learnenglish-holiday-countryside-peaceful.htm.
Mackenzie, KJD and Green, JM 1971. The cause of Color in Derbyshire Blue John banded fluorite and other blue banded fluorites. Mineralogical Magazine, December 1971, vol. 38, pp. 459-470.
Ollernshaw, AE 1964. The history of Blue John stone; methods of mining and working, ancient and modern. Published Castleton via Sheffield, 23 p.
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Filed under: minerals Tagged: Blue John, Castleton, cavern, Derbyshire, fluorite, Limestone, minerals 
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