The Blue John Cavern
The Blue John Cavern In Derbyshire
Blue John is Britains
rarest mineral first discoverd at Castleton by the Romans almost 2000 years
ago. And are the worlds only known deposits of this extremely rare and beautiful
stone.
During excavations at Pompeii two vases of Blue John Stone were supposedly unearthed, evidence therefore that the Romans not only discovered the stone but also appreciated it for its ornamental value.
The Blue John Cavern is home to 8 of the 14 known veins of this beautiful mineral.
Geology And Mineralogy
Blue John Stone is the most prized ornamental variety of Fluor-Spar (Calcium Fluoride). Differing from any other flour-spars in that it has definite banded veins of colour running through it.
Quality stone is found in veins of some three inches in thickness on average. Or in nodular forms lining the inner walls of cavities in the carboniferous Limestone o f just one hill to the west of Castleton Village.
Nodules are spherical "fungus-like" growths, composed of concentric bands of blue, purple and white or yellow fluorite, radiating from a central focal point. Massive varieties are seen to be composed of interpenetrating cubic crystals.
It has been seen that certain specimens will show signs of fluorescence on exposure to ultra-violet light, but this is the exception rather than the rule.