Derbyshire Blue John

derbyshire blue john vase with lid on display in London's Natural History Museum

 

 

Derbyshire Blue John is a rare variety of the mineral fluorite which comes exclusively from Castleton in Derbyshire, United Kingdom.  It was first discovered whilst mining for lead.

Derbyshire Blue John is a calcium fluoride mineral whose colour comes from films of oil which fell on the crystals many millions of years ago.