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The current featured stone:

 

Tenebrescent Scapolite

 

Refractive Index:  1.52-1.57 Crystal Structure: Tetragonal
 

 

 
Hardness:  6 Specific Gravity:  2.56-2.77 
 

 

 
Chemical Composition:  (Na,Ca)4[Al3Si9O24]Cl
 
Occurrences:   Afghanistan

While we are unabashed lovers of colored gems, we have to admit that Scapolite it not usually a stone which has a wide appeal.  Its most common colors in include a light violet and a straw yellow that can often make for inferior, yet more expensive,  substitutes for Amethyst and Citrine.  Add to that the fact that Scapolite's optical properties are also similar to Quartz and you can begin to see why this stone has been stuck.

This unfortunate set of circumstances changed dramatically a few years ago with the discovery of a phenomenal new variety of Scapolite.  Tenebresence is the name given to a color change induced by UV light and when a deposit of colorless Scapolite from Afghanistan was tested with UV light, the result was remarkable.  Colorless gems underwent a profound change of color to a saturated,  medium blue.  When the short-wave UV light was removed the stones immediately began to fade and returned to colorless within a few minutes.  The stone is then ready to go through this cycle again and again.

Very few gems are capable of tenebresence - Hackmanite being the usual example - and the discovery of the new Scapolite was both a welcome treat to collectors and a boon for Scapolite itself.  As the stone is a desirable rarity - the deposit did not produce a huge quantity of gem material - prices are higher than for Scapolite in other colors.  Still, they likely do not fully reflect the limited nature of the deposit and the fact that supplies are likely to dwindle.  For lovers of phenomenal stones, the unlikely treat given by Scapolite is likely to excite interest for some time.