Saturday, August 22, 2015

The Name's John. Blue John


Picture for a moment your country's most prized natural resource (besides James Bond of course ;). For us in Canada it's not too difficult, as we are blessed with many. Now imagine if that natural resource were to suddenly dry up, or at the very least, that the supply would be so scarce that only a half-ton is extracted annually. Furthermore, it would not be until 150 years later that a new deposit would be discovered. That's quite the dry spell! Perhaps only then can we begin to understand the surprise of English miners when, just a few days ago, they discovered new veins of Blue John in Derbyshire. While "Blue John" is certainly not England's most prized nor its most important resource, its popularity during the Regency-era and general scarcity certainly account for the high prices it covets at auction today. So what is Blue John and what's so special about it?

Wedge of  "Blue John", displaying beautiful banding. Photo courtesy of www.mineral-forum.com

A banded variety of fluorite (calcium fluoride), Blue John is supposedly named as such because French prospectors from the reign of Louis XVI imported the material and described it by its colors: blue and yellow (bleu, jaune). This story is not yet substantiated by records in France, but it does aptly illustrate the kind of distinct color zoning and banding that is seen in this stone, ranging anywhere from purplish blue, to yellowish cream. This particular variety of fluorite has only been found in Derbyshire, central England. Other fluorite can also be found mainly in China and the U.S.A.

A fluorite rough specimen. Photo courtesy of www.mtgms.org
While other well-known gemstones rank high on the Moh's scale, fluorite sits relatively low at 4. To give a point of reference, this is softer than man-made glass, but still harder than a human nail; coupled with perfect and very easy cleavage, fluorite is very ill-suited for faceting. This is why we generally see it fashioned into tumbled stones, cabochons; and in the case of Blue John, a significant amount of ornamental pieces were made, including vases, chess boards squares etc... It is especially the work of Matthew Boulton that would bring rise to the vases who would even grace the halls of royal homes in England.

Regency-era "Blue John" vases, circa 1810-1820. Photo courtesy of www.coulborn.com

Apart from its basic properties, fluorite is most interesting because of its ability to fluoresce when exposed to UV lighting. For those who have been to laser tag (the notoriously dark rooms that are lit with certain lights making certain items fluoresce) are actually similar to the effect seen in fluorite. This light excites the electrons within the material to a point where it must release energy in order to stabilize itself. It does so by emitting a luminescent "glow". While they are not the only gemstones that have this ability, fluorite generally has a very pronounced reaction to it. Some attribute this to the REE (Rare Earth Elements) within the material.

Tumbled fluorite before and during exposure to UV light. Excellent example of fluorescence. Photo courtesy of www.geology.com

I don't know about you, but when hearing about new discoveries like this, I have the urge to go out and explore. You never know what you'll find! 

2 comments :

  1. WOW what an amazing discovery! Do you think that it can be incorporated with other gems for jewelry?

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    1. Hi There! We totally agree with you! There are some people that choose to wear cabochons or slices of fluorite and even Blue John in jewelry. So long as it is worn only occasionally and people remember to take the proper precautions to secure the stone (due to its softness and cleavage) there should be no issues. Storing fluorite the same as most soft materials: it should be kept apart from other jewelry in order to avoid any scratching. So if you do find stones that you'd like to incorporate with fluorite and you've taken these measures, we say go for it!

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