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 Post subject: Re: Purple tourmalines
PostPosted: Fri Aug 03, 2018 3:19 am 
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Purple tourmaline is close to my heart and I have been fortunate to get to see and test the four non cuprian tourmaline discussed in this post. I also looked at a purple that had been determined to have copper by a qualified lab.

The four non cuprian tourmaline have very simlar absorption curves that do not show any signs of copper absorption. The absorption curves are dominated be what is probaby the manganese +3 peak while the much smaller iron peak in the red end of the spectrum impacts the stone's color relatively little, I think. The purples are definely reddish. The depth of the transmission window at the purple end does not appear to be exceptional and that left me wondering. Why are these tourmalines purple?

After I printed out the purples absorption curves I began to compare them with curves I have for my purples. None of my curves for cuprian purples fit the non cuprian purples curves closely. The absorption of copper +2 completly dominates the cuprian curves in most cases.

So on with non cuprian aborption curves. Now my collection of non curian purples is not rich, but the limited number of gems I have cut from probably Madagascar material did show similar curves with the the four non cuprian tourmaline. My best example of non cuprian purple is darker and smaller and not as red, but that is what I focused on.

Well I did say, probable manganese +3 curve, earlier because it finally became obvious that the probable manganese peak, which is usually around 530nm was at 550nm in the purples. This makes the transmission window wider in the purple end and is probably the reason the tourmaline are purple rather than red/pink. It would be very interesting to see if the non cuprian purples are liddicoatite rather than Elbaite. I don't think that it makes any difference whether is is Elbaite or Liddicoatite, but then I have no idea why the peak has shifted. And I have never read about the shift anywhere.

Anyone want to step up and try and get research one on an interesting tourmaline question? There are many, I am worn out from trying to get work done on the cuprian reverse Alexandrite color changer I have called Laurellite. My collection is always available for testing though the days of sending my beauties all over the world is over.

There is really little to say about the beautiful rich bluish purple cuprian tourmaline. Its tone was high and copper absorbes so much red that I do not have a strong enough light to really analyze it with my spectremeter. I did enjoy seeing it and I am sure that it is cuprian.

Bruce


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 Post subject: Re: Purple tourmalines
PostPosted: Sat Aug 04, 2018 11:58 am 
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ruby302 wrote:
newark, we havent conversed in months-why ruin a good thing!! #-o Ur afraid of appraisers because U GOT NOTHING, EXCEPT BY MISTAKE!- :evil:
When you tell one of our well respected, knowledegable G.O. members to staple his mouth shut , I'm going to respond. Your obsession with these worthless, inflated appraisals is borderline insanity. Weren't you thrown off other forums for this very reason.This is only a disservice to any new members that think you know what you talking about. Your statement that I'm afraid of appraisers and have nothing-what does that even mean? Only with one of your well respected appraisers can one belt out a couple karaoke songs while his stones are being checked. Have you ever seen a non commercial quality stone? Here are a couple with rough and cutting by G.O. members. Don't try to silence the people that are knowledgeable.


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 Post subject: Re: Purple tourmalines
PostPosted: Sun Aug 05, 2018 2:37 am 
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bruce_tourm wrote:
...

Interesting. Thanks for all the info, Bruce!


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 Post subject: Re: Purple tourmalines
PostPosted: Tue Aug 07, 2018 12:18 pm 
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Very apt!


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 Post subject: Re: Purple tourmalines
PostPosted: Tue Dec 11, 2018 9:37 am 
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After receiving the reddish purple set of stones pictured above and a blue purple that had already been determined to be copper based, I checked them with my spectrometer. By eye I would speculate that the reddish purple stones did not have a significant amount of copper and my spectrometer confirmed my speculation. The blue purple turned out to be so highly toned, with a steep angles on the pavilion, that I was unable to get a good absorption numbers on it. But it certainly had a beautiful color that I am sure indicates copper at a high enough concentration to be a significant chromophore. I think it was not heated because of its flawed nature. (I would keep it natural even if it was eye clean, but that is another story.)

After the results from the spectrometer, we had a long discussion over heating, recutting and finally selling the gemstones. The really important blue purple gemstone has a weight retention cut that would loose a lot of weight in recutting in my opinion. But I really do very little recutting and the decision on recuttung will be handled by others.

In the middle of our discussions I was offered one of the reddish purples as a gift and I gladly accepted since the stones are different and I love that. (I won't get into an emotional debate about which colors in tourmaline I love the best, but anything in tourmaline I have not seen is right in the front of the line!)

Well I have recut the reddish purple round and despite being significantly included it is a bright flashy gemstone that has a secrete. When the light is right it is transformed from pink/red in incandescent light to a great purple under the kind of bright diffused natural light you can get on grey days and after the sun goes down in the evening. In other words you need the bluish side of natural lighting to reveal its true purple side. When the sun is about, you get a much redder purple,

I am reluctant to call the stone a "color changer" because all purples are shifters to a degree and while the choice of lighting uses natural light for the bluer source, the stone has not been tested under laboratory conditions. Whatever label you put on it, it is another wonderful example of the dynamic world of color in tourmaline. Oh and the CIE color determination program on the spectrometer says the tourmaline is a slightly bluish red. A determination I might question by my eye.

Bruce


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 Post subject: Re: Purple tourmalines
PostPosted: Sat Feb 02, 2019 5:37 am 
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What do you think of this report? This was a parcel of pink tourmaline.

How do you even define paraiba? Is it region or color?


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 Post subject: Re: Purple tourmalines
PostPosted: Sat Feb 02, 2019 12:59 pm 
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Terming a gem "Paraiba-type tourmaline" is considered to be a function of the presence of copper and manganese in its chemistry coupled with a description of its color as being "vivid".
"Vivid" is somewhat of a subjective description.

See this post by Bruce Frye:
viewtopic.php?f=6&t=22253

The GIA's position is as follows:
Quote:
“Paraíba”-Type Copper-Bearing Tourmaline from Brazil, Nigeria, and Mozambique: ...
Gem-quality bright blue to green “Paraíba”-type Cu-bearing tourmaline is now known from deposits in Africa (Nigeria and Mozambique), in addition to three commercial localities in Brazil (in Paraíba and Rio Grande do Norte States). Stones from these new localities have been mixed into parcels from the original Brazilian Paraíba occurrence. The Nigerian and Mozambique tourmalines that show saturated blue-to-green colors cannot be distinguished from the Brazilian material by standard gemological testing or on the basis of semi-quantitative chemical data (obtained by EDXRF analysis). However, quantitative chemical data obtained by LA-ICP-MS show that tourmalines from the three countries can be differentiated by plotting (Ga+Pb) versus (Cu+Mn), (Cu+Mn) versus the Pb/Be ratio, and Mg-Zn-Pb. In general, the Nigerian tourmalines contained greater amounts of Ga, Ge, and Pb, whereas the Brazilian stones had more Mg, Zn, and Sb. The new Cu-bearing tourmalines from Mozambique showed enriched contents of Be, Sc, Ga, Pb, and Bi, but lacked Mg.






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