Blue John: Remarkable fluorite from a limestone cavern

Steven Wade Veatch (USA) 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 7.5cm 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. Fig. 1. Located in limestone, deep witihin the Treak Cliff and Blue John Caverns, Blue John has been mined for its beautiful colours for centuries. (D Veatch specimen, photo by S Veatch.) Blue John was first discovered about 2,000 years ago when the Romans mined lead and … Read More

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