Blue John Fluorite is one of the rarest and most expensive types of fluorite in the world.
Coming only from a single location in the UK, it brandishes a beautiful bluish-purple color with bands that can be white or yellowish alongside darker blue-purple bands.
It’s a highly valuable mineral for its opulence in decorative and ornamental designs.
The purple color is a mystery, no one quite knows where or how it forms.
Even after centuries of use, all we can surmise is how it loses color once exposed to higher heat temperatures.
This makes it even further unique in that it comes from deep caverns that have hot fluid running over its surface.
What Is Blue John Fluorite?
Blue John Fluorite is a semi-precious mineral with the chemical formula CaF2.
Also called Derbyshire Spar, it’s a very rare form of fluorite.
It formed during the late Carboniferous and Early Permian periods, when limestones sat at a depth of 1.9 miles (3 kilometers).
Formed by Hot Saline Fluid
There are hot fluids coating the fractures, cavities and caves, which deposit this mineral in veins by layers of crystals that precipitate from the these fluids.
This crystallizes from a highly saline fluid at temperatures ranging between 194°F and 248°F (90°C and 120°C), or even higher.
Unknown Purple Colors
But the mystery of this stone comes from the fact that no one can place the origin of the bluish-purple color.
There are theories that indicate a rare phenomenon via crystal lattice dislocation, but no one has yet proved this.
Known History of Blue John Fluorite
The earliest known mention of Blue John Fluorite comes from a letter in 1766.
It notes a lease from one Lady Mazarine.
There’s yet another mention of it in a 1768 letter from a man named Matthew Boulton who attempted to either lease or purchase the mines for the mineral’s ornamental value.
Where Do You Find Blue John Fluorite?
There is only one place you can find Blue John Fluorite and that’s at Treak Cliff Cavern and Blue John Cavern at Castleton in Derbyshire of the United Kingdom.
There are recent discoveries of it in Vestland, Norway registered in 2021 but these are very small deposits.
How Do You Identify Blue John Fluorite?
Blue John Fluorite is very unlike other types of fluorite.
It has perfect cleavage in all four directions and well-formed coarse-sized crystals.
It ranges between being transparent and translucent but has a vitreous luster.
It sits at 4 on the Mohs Scale of Hardness.
There are often white or yellowish streaks that can contain dark blue, purple and reddish bands.
A few can even be colorless.
The bands appear crossed and crooked which make them unmistakable.
Experiment with Heat, Irradiation ; Light
One test you can do is to put it in the oven for a few hours.
You set the heat somewhere between 212°F and 302°F (100°C and 150°C).
If it loses its color, it’s a Blue John Fluorite.
It will totally lose all color at 392°F to 572°F (200°C to 300°C).
Irradiation will completely restore the color, which is what makes the purple color of the mineral an interesting facet.
When most stones lose their color, it doesn’t come back under any circumstances.
But, Blue John’s color will.
Regardless, because of this color instability, it will permanently lose color when exposed to heat and light for too long of time.
Does Blue John Fluorite Look Like Any Other Materials?
Because of restrictions on mining efforts of Blue John Fluorite in the UK, it now acquires similar looking stones from China such as Baryte and Galena.
Plus there are similar blue fluorite stones in the UK, the Ardennes region in Belgium and Cave-in-Rock of Illinois as well as Mexico.
Therefore, there’s a host of other materials, minerals and crystals it can look like.
But, the ones from China contain the blue band very much akin to Blue John Fluorite.
While it is a fluorite, the banding is straighter than Blue John, which means there are other compounds.
For What Do People Use Blue John Fluorite?
Since the 19th century, Blue John Fluorite has great use for mostly decorative purposes.
It either adorns or comprises candelabras, knife handles, chalices, goblets, clocks, jewelry, fireplace panels, plaques, tiles, vases and statues, such as the panther commissioned by King George III.
Pretreatment before Working
But, Blue John Fluorite must undergo treating prior to fashioning into objects for use.
Because it has a rating of 4 on Mohs, it’s very soft and breaks easily.
So, before working, it must sit for year completely exposed to air.
The mineral then gets heated in the oven and placed in a bowl of hot epoxy resin.
Once again, it heats but this time in a vacuum oven.
Doing this drives out air from the stone’s diminutive pores and replaces it with the resin.
The impregnated epoxy fills the thin walls and reinforces the fragile crystal structure.
This process makes Blue John Fluorite ideal for cutting and polishing.
In its natural state, it crumbles under cutting.
What Is the Meaning of Blue John Fluorite?
Because of its rarity and sole location, the whole of Europe has held this stone in high regard.
Even the occupying Romans deemed it as a source of protection from drunkenness when consumed from a chalice or bowl made of it.
Known as the either the “Genius Stone” or the “Enigma Stone,” people believe it acts as a catalyst for soul inspiration, personal growth and understanding the world.
It represents learning, enlightenment, finding solutions and healing on various levels.
Blue John Fluorite is a wonderful mineral with many creative and artistic possibilities.
It’s crystalline structure contains a mysterious purple that scientists have yet to understand. It can disappear upon heating and reappear upon irradiation.
It’s beautiful with a host of potential uses in everything from architectural tiling to jewelry.
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