Novembr 16-18—COLUMBIA, SOUTH CAROLINA: Annual show; The Columbia, SC Gem and Mineral Society; Fri. 10-6, Sat. 10-6, Sun. 12-5
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 Post subject: Opinions on a tourmaline crystal needed
PostPosted: Sat Apr 07, 2018 6:27 pm 
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A fellow emailed me because he is sizing down his crystal collection.
His question was, "What would be a fair price to ask for this indicolite?" 90+ carats

Chime in!
Click on the pic to enlarge.


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 Post subject: Re: Opinions on a tourmaline crystal needed
PostPosted: Sat Apr 07, 2018 9:02 pm 
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Is it clean cuttable rough, or specimen material?


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 Post subject: Re: Opinions on a tourmaline crystal needed
PostPosted: Sun Apr 08, 2018 7:01 am 
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It looks kind of flat what are the dimensions?

Jim


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 Post subject: Re: Opinions on a tourmaline crystal needed
PostPosted: Sun Apr 08, 2018 5:21 pm 
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https://youtu.be/pbnhHb_X450 150 ct. Ocean blue tourmaline rough cut to 56 ct. finished stone. Cutter Vlad Yavorskyy.

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 Post subject: Re: Opinions on a tourmaline crystal needed
PostPosted: Sun Apr 08, 2018 5:34 pm 
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Some new updates:


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 Post subject: Re: Opinions on a tourmaline crystal needed
PostPosted: Mon Apr 09, 2018 5:52 pm 
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What makes this tourmaline an indicolite rather than paraiba? In other words, what would be the deciding factor? Presumably, both contain copper. But would the gradation and saturation of the blue hue, as per GIA for example, be the dividing line?

I would think the price for the cut stone per carat would be much higher if it could be fairly graded a paraiba.


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 Post subject: Re: Opinions on a tourmaline crystal needed
PostPosted: Mon Apr 09, 2018 6:05 pm 
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I was not aware that copper was a chromophore in indicolite.
I don't think it is.


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 Post subject: Re: Opinions on a tourmaline crystal needed
PostPosted: Mon Apr 09, 2018 7:11 pm 
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Tygurrr-I wrote:
Presumably, both contain copper.

No. Iron is the typical chromophore for blue tourmaline. Copper coloration is very unusial amd tends to produce a richer purer cyan color, which is the crux of why cuprian tourmaline is so valued.


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 Post subject: Re: Opinions on a tourmaline crystal needed
PostPosted: Mon Apr 09, 2018 9:54 pm 
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No, that does not look cuprian to me, but traditional indicolite.

I have bought a number of kilos of fine African tourmalines lately. What I don't have is a good understanding of the rough piece in question. It looks more like a display crystal than a cutting piece to me. I do not trade in collector xtls so do not feel comfortable with price on this.


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 Post subject: Re: Opinions on a tourmaline crystal needed
PostPosted: Tue Apr 10, 2018 1:44 am 
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IMHO the crystal growth structure will be a problem when cutting. Where the daughter crystals have attached are weak planes and are likely to fracture or split off during cutting, or even some time after it's been cut and polished.

If you cleaned off all those daughter growths, you wouldn't be left with much of the original stone. I'd recommend keeping this as a specimen rather than cutting it.

-Allan

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 Post subject: Re: Opinions on a tourmaline crystal needed
PostPosted: Tue Apr 10, 2018 4:12 am 
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Barbra Voltaire wrote:
I was not aware that copper was a chromophore in indicolite.
I don't think it is.



Hmm, you're right. Here is a better source than the one I initially ( and lazily) skimmed, if anyone is interested:

https://www.gia.edu/doc/Spring-2017-Gem ... maline.pdf


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 Post subject: Re: Opinions on a tourmaline crystal needed
PostPosted: Wed Apr 11, 2018 9:12 pm 
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Thanks Tygurr.


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