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Blue John

Blue John Stone is a very rare semiprecious mineral found in only one place in the entire world, Castleton, on a hillside near Mam Tor. It gives Castleton its nickname of 'Gem of the Peaks.'

Exploring the cave systems of Castleton for lead, miners came upon the mineral, a form of fluorite with a name which derives from the French Bleu Jaune which means blue yellow. The story goes that Blue John was exported to France, where it was used by workers during the reign of Louis XVI, but there is no archival record this.  An alternative name for the mineral derives from an old miners name for the zinc ore sphalerite, which they called Black Jack.  Another name comes from the Cornish miners who began working the Derbyshire lead mines in the late 1780s. The name Blue John is used for several rocks in Cornwall, including flourspars, and comes from the Cornish language word 'bluejenn', in Old Cornish 'blodon', a flower, blossom or bloom.

Chemically it is calcium flouride, which has been coloured by films of oil deposited on the crystals millions of years ago. It is sometimes said that it was discovered by the Romans. However, the earliest sourced story is William Adams 1843 book called 'Gem of the Peak'. Although the Romans certainly mined lead in Derbyshire, there is no evidence they encountered the Blue John veins.

It is prized for jewellery and ornaments and has been worked so since 1750, and can be found in great collections housed in places such as the Vatican, the White House and Windsor Castle. It's not clear if a mistake in drying the stone caused by the discovery the old craftsman who dried the blue John Stone, but it was noticed it changed colour, from pink and red, but great care needs to be taken because at 230°C, when the stone changes colour, gases produced which could explode and destroy the whole piece.

The stone is mined in the caverns of Castleton, magnificent show caves and some of the most popular tourist attractions in Derbyshire. The stone is easy to see and many of them formations are well lit for visitors to the cavern. Of the four show caves only Treak Cliff and Blue John have veins of the Blue John Stone. The former mines about 500 kg each year and the raw Blue John produced is kept within Castleton, where small articles, mainly jewellery, are worked and sold.

The Blue John Cavern in the Peak District is a series of caverns considered to be the finest range in Great Britain.   Our Cavern Tours are of immense educational interest showing clearly how the caverns are formed in limestone strata and how the limestone itself had much earlier been formed by the deposits on the floors of great oceans which have long since receded, as the fossilised remains of marine animals now show.   The Cavern is well illuminated by electric...
The Original Blue John Cavern , Craft Shop and Cafe- Castleton
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