Blue John Cavern
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The Blue John Cavern is one of the four show caves in Castleton, Derbyshire, England. The others are Peak Cavern, Treak Cliff Cavern and Speedwell Cavern.
Blue John seams in the cavern
Entrance to Blue John Cavern
Fluorite
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Fluorite is the mineral form of calcium fluoride, CaF2. It belongs to the halide minerals. It crystallizes in isometric cubic habit, although octahedral and more complex isometric forms are not uncomm
Blue John Cavern
…Alfred Brothers. In the UK Blue John, or "Derbyshire Spar", is found only in Blue John Cavern and the nearby Treak Cliff Cavern. It is a type of banded fluorite. The most common explanation for the name is that it derives from the French bleu-jaune, meaning 'blue-yellow', but other derivations have been suggested…
The structure of calcium fluoride CaF2.
A closeup of fluorite surface
Blue Fluorite, from Shihe District, Henan Province, China