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Opinions on a tourmaline crystal needed
https://www.gemologyonline.com/Forum/phpBB2/viewtopic.php?f=8&t=24369
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Author:  Barbra Voltaire, FGG [ Sat Apr 07, 2018 6:27 pm ]
Post subject:  Opinions on a tourmaline crystal needed

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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Author:  1bwana1 [ Sat Apr 07, 2018 9:02 pm ]
Post subject:  Re: Opinions on a tourmaline crystal needed

Is it clean cuttable rough, or specimen material?

Author:  JCD [ Sun Apr 08, 2018 7:01 am ]
Post subject:  Re: Opinions on a tourmaline crystal needed

It looks kind of flat what are the dimensions?

Jim

Author:  Nicky Newark [ Sun Apr 08, 2018 5:21 pm ]
Post subject:  Re: Opinions on a tourmaline crystal needed

https://youtu.be/pbnhHb_X450 150 ct. Ocean blue tourmaline rough cut to 56 ct. finished stone. Cutter Vlad Yavorskyy.

Author:  Barbra Voltaire, FGG [ Sun Apr 08, 2018 5:34 pm ]
Post subject:  Re: Opinions on a tourmaline crystal needed

Some new updates:

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Author:  Tygurrr-I [ Mon Apr 09, 2018 5:52 pm ]
Post subject:  Re: Opinions on a tourmaline crystal needed

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.

Author:  Barbra Voltaire, FGG [ Mon Apr 09, 2018 6:05 pm ]
Post subject:  Re: Opinions on a tourmaline crystal needed

I was not aware that copper was a chromophore in indicolite.
I don't think it is.

Author:  Stephen Challener [ Mon Apr 09, 2018 7:11 pm ]
Post subject:  Re: Opinions on a tourmaline crystal needed

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.

Author:  1bwana1 [ Mon Apr 09, 2018 9:54 pm ]
Post subject:  Re: Opinions on a tourmaline crystal needed

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.

Author:  gembug [ Tue Apr 10, 2018 1:44 am ]
Post subject:  Re: Opinions on a tourmaline crystal needed

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

Author:  Tygurrr-I [ Tue Apr 10, 2018 4:12 am ]
Post subject:  Re: Opinions on a tourmaline crystal needed

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

Author:  Barbra Voltaire, FGG [ Wed Apr 11, 2018 9:12 pm ]
Post subject:  Re: Opinions on a tourmaline crystal needed

Thanks Tygurr.

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