|Hardystonite: fluorescent blue-violet, SW
Willemite: fluorescent green, SW
Calcite: fluorescent red, SW
Franklinite: non-fluorescent (black areas)
When fluorescent minerals are exposed to the weather, they develop a "rind" of darkened material that does not fluoresce very well. When a specimen is large enough, one takes a hammer and a sharp chisel to the piece in order to break off the "rind" and expose fresh surfaces for display.
This is not possible in the case of a chunk that's thinner than about 2 centimeters... but hardystonite does not grow on trees, so it seems a tragedy to throw a piece of it away (or let it weather away to nothing on the dump). So what is there to do? Cut it into a cabochon so you can bring out the fresh surfaces, that's what! Many a fluorescent treasure can be rescued this way.
Note the nice, velvety blue-violet fluorescence of the hardystonite. The franklinite provides a nice contrast. This cabochon is currently in a private collection. I sold it on ebay some time ago.
Raw material was collected and cabochon was cut, polished, and photographed by C. Thorsten. The purple reflection you see on the stone is the glow of the lamp reflecting off the highly-polished surface.
I have some more cabochons for sale (also cut and polished by me) at the above website.
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