A blue or purple banded variety of fluorite found in Derbyshire.
（德比郡产的）带蓝色（或紫色）纹理的萤石，蓝约翰
Example sentencesExamples
It is likely that they were searching for deposits of lead ore and struck upon an outcrop of Blue John by chance.
And please note: because of the nature of Blue John we cannot guarantee that the patterning in the stone you receive will be exactly the same as that shown in the photograph above.
Many of our Blue John items can also be made in other stones like Jade, Turquoise or Mother of Pearl.
The name Blue John very likely was made up by John Kirk and Joseph Hall who worked the mines in the 18th Century.
It looks like at some point the slag from the mine was dumped into this hole in small quantities, and as a boy I found many chunks of Blue John down there.