October 3-7—JOSHUA TREE, CALIFORNIA: Annual show; Sportsmans Club of Joshua Tree
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 Post subject: Re: more tourmaline NIR
PostPosted: Tue Sep 20, 2011 12:52 pm 
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A very nice thread--thanks to both of you for discussing the results of your tests!

This very much appeals to my nerdy side. While I came here for the faceting discussions, I might turn into an aspiring gemologist if I'm not careful ;)

--Eric

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 Post subject: Re: more tourmaline NIR
PostPosted: Tue Oct 04, 2011 1:40 pm 
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Looking back at the spectrum of the red tourmaline (number 47), the G&G article associates the absorption that peaks at > 900 nm with manganese, while the peak at 700 nm is associated with iron. However, the G&G article does mention another possible Mn absorption occurring at 700 nm. So there is some confusion.

Naturally we begin to wonder if the > 900 nm absorption peak can exist without the 700 nm peak. Bruce sent me his two most likely candidates. The first candidate is a pink stone.

Attachment:
pink pic.JPG
pink pic.JPG [ 24.99 KiB | Viewed 2224 times ]

Bruce's spectrum of this stone shows no peak at 700 nm, but it looks like the absorption is on the rise up to the 850 nm limit of his spectrometer. So this is the spectrum I recorded.

Attachment:
pink.JPG
pink.JPG [ 17.61 KiB | Viewed 2224 times ]

Overall, the NIR spectrum between 800 - 1000 nm is relatively flat, with some small bumps and depressions. So I don't think it is quite what we were looking for.

The other red stone Bruce sent shows spectrum across the NIR range that is, if anything, even more flat.

So examining Bruce's most promising samples, I didn't find a > 900 nm absorption peak when the 700 nm peak is missing.


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 Post subject: Re: more tourmaline NIR
PostPosted: Tue Oct 04, 2011 5:10 pm 
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Thanks Brian,

We may have reached the limit of my collection, I will try and look at a larger sample of tourmaline. Not finding something can be almost as much fun as finding something. Whether the 900+nm peak ascribed to manganese +3 is tied to the 700 nm curve or not, where does all the pink/red come from in my collection of pink/red tourmaline in my collection that show neither the 700nm nor 900+nm absorption curves? If they are also colored by manganese +3 the chromophore must be in a different location in the crystal latice of the tourmaline or have some other electronic environment.

Bruce


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 Post subject: Re: more tourmaline NIR
PostPosted: Wed Oct 05, 2011 9:46 am 
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By the way, I forgot to mention the pink stone is a nice color, falling into that "hot" pink category.

bruce_tourm wrote:
We may have reached the limit of my collection,

Now that is saying something.

bruce_tourm wrote:
where does all the pink/red come from in my collection of pink/red tourmaline in my collection that show neither the 700nm nor 900+nm absorption curves?

A mystery, to be sure.


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