Post subject: Opinions on a tourmaline crystal needed
Posted: Sat Apr 07, 2018 6:27 pm
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Joined: Sun Oct 16, 2005 12:22 pm Posts: 21602 Location: San Francisco
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
Post subject: Re: Opinions on a tourmaline crystal needed
Posted: Mon Apr 09, 2018 5:52 pm
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Joined: Sun Aug 21, 2016 7:39 am Posts: 228 Location: Long Island NY, USA
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.
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.
Post subject: Re: Opinions on a tourmaline crystal needed
Posted: Mon Apr 09, 2018 9:54 pm
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Joined: Thu May 12, 2016 2:18 am Posts: 1542
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.
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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