Fluorite – Will It Fluoresce or Not?
Fluorite is a mineral that is used as a gemstone. As its name implies it is often fluorescent under ultra violet light. The Blue John variety is often used for carvings. There is a common misconception that fluorite always forms in little octahedral shapes.
Does fluorite have an octahedral habit?
Fluorite can form in an octahedral habit naturally, but… its most common habit is the cube and often interpenetrant cubes. Vendors at gems shows are aware that people love to collect the many colours of fluorite in little octahedral shapes, so they are cleaved into octahedral shapes. Fluorite is transparent to opaque and comes in colourless, blue, violet, green, yellow, orange and pink.
These cubes of fluorite can be found at the Smithsonian Natural History Museum in Washington, D.C.
Fluorite is faceted into beautiful gemstones, but it is relatively soft compared to other gemstones. It is only a 4 on the Mohs mineral hardness scale, quartz and dust are a 7. This means that fluorite would be better suited for pendants and earrings, rather than a ring where is might easily be damaged.
The cubes of purple fluorite on the left are fluorescing blue under long wave ultra violet light. Although the name implies that all fluorites are fluorescent, this is not the case. Even specimens from the same locality will fluoresce to varying degrees or not at all. Below the octahedrons of green fluorite also fluoresce blue under LW UV light.
Blue John is the banded (striped) variety that is often carved. This specimen of Blue John Fluorite from Derbyshire is at the Great North Museum. This museum is in Newcastle upon Tyne in North East England. Fluorite is found world-wide; Blue John is from Derbyshire, UK.
The name “Blue John” comes from the French “bleu et jaune” for blue and yellow describing the colour.
I was so disappointed when my first piece if fluorite did not fluoresce! It turns out that the Blue John variety of fluorite does not fluoresce or only very, very slightly.
This group of fluorite specimens can be found at the Royal Ontario Museum in Toronto.
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