Gem Profile- Derbyshire Blue John

by Judy Ellis

While surfing the internet for more beautiful and unusual minerals and gems, I came across another rare stone found only in the Peak District of England near Castleton, Derbeyshire. This rare blue and yellow banded fluorite is known as Blue John.

The name likely comes from the French words for the stone's colors, bleu et jaune, meaning blue and yellow. There are no records of the French mining it or exporting it, though.

A more likely explanation is that miners coined the name themselves to distinguish this banded fluorite from the zinc ore called Black Jack, which was mined in the same region.

What is Blue John?

Originally mined by the Romans more than 2000 years ago for smelting and ornamental purposes, Blue John has been admired for centuries.

Pliny the Elder referred to the stone as Murrhine and even wrote about a Roman consul who drank from a Blue John goblet and gnawed at its rim.

Pliny described Murrhine as a stone with a great variety of colors, including shades of purple and white with blended tones. It was commonly carved into drinking vessels.

Two such cups were discovered in Roman graves near the border of Turkey and Syria, carved from Blue John. They now reside in the British Museum.

How do we get Blue John?

Blue John is mined today from two caverns in the Peak District, the Blue John and Treak Cliff caverns. These caverns sit within a large underground network beneath the rolling hills of Derbyshire, Staffordshire, and Cheshire. They serve as both a local tourist attraction and an active mine.

Blue John is found in veins about three inches thick along the limestone cavern walls, occurring in rakes, scrins, and pipes.

Blue John Veins in the Blue John Cavern. Photo Courtesy of Blue John Cavern.

Rakes are vertical with areas nearly 10 feet wide at points and can be followed for often more than a mile. Scrins are veins that branch off a rake and are smaller in width and shorter than a rake. A pipe is an area between rakes that is horizontal and irregular often occurring as nodular masses.

While fluorite occurs worldwide and in various colors from pink, purple and blue to clear and yellow, only the banded fluorite Blue John is found in the Peak mining district of Derbyshire.

Fluorite Vein of Blue John Cavern. Photo courtesy of Blue John Cavern.

Blue John is a soft stone at only 4 on the Mohs scale. It has perfect cleavage and is easy to carve and is rarely faceted. Lapidarists option to form the stone en cabochon to better show the beautiful color variation of the stone.

Take a trip to see Blue John:

If you're planning a trip to the United Kingdom leave a day for a trip to the Blue John caverns in Derbeyshire.

The caverns are open year-round except for Christmas and New Years Day.

The caverns are well-lit and debris free for tours and dogs are always welcome.

Blue John cavern entrance today.

There is some interesting history surrounding the mine with bones over 4.000 years old being found in the mine.

Those are on display for all to view.

There is also a story of the most valuable vein of Blue John that had been lost for over 70 years only to be rediscovered under an old piece of carpet in the mud.

You can also explore the beautiful stalactites in the Treak Cliff cavern and learn more about the history of the caverns, mining and Blue John.

Treak Cliff Cavern

Gem Profile- Derbyshire Blue John

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