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Greenland sodalite - Thermoluminescence

24.1.2015

While experimenting with Afghan sodalite, and after discussion on FB, I decided to try Greenland sodalite and see if it was thermoluminescent. That was the natural question raised by members of the FB group.  Very interesting results!

 

I pulled out several examples of the varieties found in the Ilimaussaq Complex.  Laid them out on a heavy metal sheet, let me eyes become dark-adjusted, and hit them with a MAP torch.  Only one variety was thermoluminescent, glowing a bright yellow.  Amazing.  So then I thought, let's check it in boiling water (should have done that first).  No luminescence.  But I noticed that it was slightly tenebrescent - wow!  Fade and repeat.  Yep, boiling water causes it to tenebresce; for those familiar with what we call "Red Sodalite", the tenebrescence was like LW tenebrescence - a nice light purple.

 

The image on the left is as it looked coming straight out of the boiling water.  The image on the right is how it looked before it went into the pot and after I faded it for a few seconds with a bright light.  No UV hit this rock between these two pics.

 

I next proceeded to take pics of the rock's thermoluminescence.  This is when I learned that it's a one-shot deal.  No amount of heating would coax any kind of glow out of this little rock.  So I went ahead and took the rest of the pics (SW, LW, and Natural).  No tenebrescent pic as it seems that all my heating destroyed the tenebrescence (this was confirmed in previous testing).  The tenebrescent ability was shot, and the fluorescence changed somewhat - the rock is now a brighter yellow under both SW and LW (fluorescent pics below):

 

 Moving on... Now that I know that the thermoluminescence is a one-shot affair I carefully selected another piece of the same variety (this is a pricey experiment ;-)).  Below are three photos.  The first is the rock under natural light, unheated or exposed to UV.  The 2nd pic is my first attempt to capture the thermoluminescence.  I set my camera exposure settings to what I thought would be accurate, heated the rock at the bottom with my torch then extinguished it, and snapped the pic.  I was a little off in my settings and the exposure was too short.  So - let's try it again!  This time I heated the rock from the top with a longer exposure (f11, iso400, 3 secs).  Voila!  A nice bright yellow, exactly as the rock looks when the torch is removed.  Interestingly, note how the bottom of the rock is no longer thermoluminescent; the first heating try ruined that part of the rock.

 

 I am now done ruining my inventory.  I will let people smarter than I figure out what all this means....

 

 

 

 

 

 

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