Blue John is a special variety of fluorspar with beautifully arranged bands of colour ranging from the deepest blue-black, through shades of purple and blue, to the purest white. Castleton in the Peak District is famous for its collection of caverns which have been the only known source of Blue John throughout the world for hundreds of years.
The mineral has been mined for use in jewellery and ornamental pieces ever since it was first discovered in Millers Mine (now Treak Cliff Cavern) around 1750. Mining continues to this day, although on a much lower scale in order to preserve the resource for as long as possible. The caverns are now open to the public and protected for future generations.
A seam of Blue John Stone is visible in the Witch's Cave, shown in the image above. Starting in the pillar on the left (which has been left to support the roof) it runs almost horizontally to the right. Other areas containing the tell-tale purple-blue colouration are also visible.
I'd like to thank the friendly staff at Treak Cliff Cavern for kindly allowing access to the Caves. For more information about Blue John Stone and the Castleton caverns please visit www.bluejohnstone.com.
