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.

Fluorite octahedrons by Orbital Joe

Flickr Photo by Orbital Joe

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.

Cubes of Fluorite at the Smithsonian

Photo by J McKercher

These cubes of fluorite can be found at the Smithsonian Natural History Museum in Washington, D.C.

Cubes of Fluorite

Photo by J McKercher

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.

Faceted and rough fluorite

Photo by J McKercher

Fluorescent Fluorite

Fluorite cubes fluorescing

Flickr Photo by Orbital Joe

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.

Octahedrons of Fluorite Fluorescing

Flickr Photo by Paul Garland

Blue John

Clue John Specimen from Great North Museum

Flickr photo by Michael Coleman

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.

Fluorite specimens at the ROM

Photo by J McKercher

This group of fluorite specimens can be found at the Royal Ontario Museum in Toronto.

Your Input (Join our poll or scroll down and leave a comment) – Emerald is winning the poll!

I plan to introduce different gemstones alphabetically.  I will start with “A” (Ammolite) and see where it leads me.  Leave a comment and let me know if you have a favourite gemstone that starts with the letter “G”.  Take the poll!  Can you name a reference to a gemstone in a song, movie or book?

About Jen McKercher

A passion for gemstones drives Jen to learn as much as she can about the wonders of gemstones and how they enhance our lives. Jennifer McKercher taught gemmology at the Canadian Gemmological Association.

Posted on July 27, 2011, in Individual Gemstones and tagged , , , , , , . Bookmark the permalink. Leave a comment.

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