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 Post subject: The challenge of Paraiba rough
PostPosted: Sat Mar 28, 2020 9:03 pm 
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This week I received a small parcel of what is supposed to cuprian "Paraiba" Tourmaline form Africa to consider purchasing. The lot consists of fairly clean stones ranging is size from 1 gram up to almost 8 grams. All the stones are the typical very dark purple color aluvial stones that are typical of the copper bearing Tourmalines from this area.

However, in the last couple of years there has been a significant production of tourmalines from this area that don't have copper, or have insufficient copper to heat to the desired cyan blue color. Because of this I don't buy cuprian tourmaline unless I get the opportunity to test for copper myself.

The images below demonstrate the issue rather well. The Third image is a graph from my GLSpectrometer that shows two spectra. The top one in red is my reference African Purple Cuprian Tourmaline. The bottom black spectra is the sample being tested. As you can see, both spectra show a nice strong peak near 920nm that indicates the presence of copper. This is what you want to buy.

The second image shows my red reference spectra once again, and a black spectra of another stone being tested. Notice that it has no peak in the 920nm are indicating no copper. This is not what you want to buy.

The first picture shows the lot divided into sub-lots one having copper, one not. As you can see, there is a significant portion of the lot that does not contain copper and is of a much lower value.

This presents two problems. The Africans who sent the stones have no way of determining for themselves whether copper is present or not. They have neither the training, nor the equipment to do so. Since the stone all came from the same place, and look identical they are all "Paraiba" in their eyes. Therefore they all have the same value. In fact they paid the same price for them and need to sell based on that. This makes agreeing on a fair price difficult, and often impossible.

This situation also means that when I am in the bush without access to my equipment i cannot buy the purple Paraiba rough with any degree of confidence.

I saw many people in Tucson this year, and last make major financial mistakes because of this situation.

Now add in all the excellent, and cleverly constructed fake rough, and treated rough, and you can see that being a buyer of rough in the bush is indeed becoming a treacherous business. Bit it is so much fun!!!

Anyway, I thought some of you would enjoy seeing some of the challenges we face these days.


Attachments:
File comment: Sorted Parcel
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CopperSorted.jpg [ 1.04 MiB | Viewed 446 times ]
File comment: Has No Copper
CopperNo.jpg
CopperNo.jpg [ 2.75 MiB | Viewed 446 times ]
File comment: Has Copper
CopperYes.jpg
CopperYes.jpg [ 1.35 MiB | Viewed 446 times ]
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 Post subject: Re: The challenge of Paraiba rough
PostPosted: Sun Mar 29, 2020 12:49 pm 
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Both samples appear about the same color.
Usually the tourmaline found in Nigeria not only has a relatively low copper content, it also typically has a very low iron and titanium content.

I suspect the color of this material is not necessarily the result of a lack of copper,but a lack of manganese+3 being the primary chromophore imparting the purple color.

If the saturated purple color is the result of a combination of elements which are not altered by heat it would explain why heat does nothing.


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 Post subject: Re: The challenge of Paraiba rough
PostPosted: Mon Mar 30, 2020 11:16 pm 
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This thread reminds me... Ive been meaning to send you a PM. I'll do that shortly.

Thanks for sharing what you observed in this parcel!


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 Post subject: Re: The challenge of Paraiba rough
PostPosted: Tue Mar 31, 2020 10:57 pm 
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Interesting! Thanks 1bwana1!


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 Post subject: Re: The challenge of Paraiba rough
PostPosted: Mon Apr 06, 2020 12:01 pm 
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I see my question has been dismissed.
So, I'll ask again.
How much of the color of this material has anything to do with copper?
I suspect, very little, if any.

A client of mine brought over a stone with a lab report indicating the presence of copper and it was identified as "paraiba type" by the lab.
The color of the material could be best described as very dirty dish water.
IMO the copper was of no consequence.


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 Post subject: Re: The challenge of Paraiba rough
PostPosted: Mon Apr 06, 2020 2:45 pm 
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Not meaning to ignore you Barbra. It is just that I have only a field level understanding of this from working with these types of tourmalines. Someone who has spent the time researching this would be a better person to answer.

There are so many different colors of tourmaline that contain copper. The greenish and brownish copper bearing tourmalines don't improve color with heating. But they often still have that "glow" Copper seems to impart to a stone, and still gets a premium price.

The copper seems to be responsible at least in part for the cyan/turquoise color that Paraiba is famous for. The stones that start off purple/red/brown in color respond to heating differently depending on whether there is copper present.

If they don't have copper , normally you can heat these purple/red/brown color stones and remove the brown or with enough heat fade them all the way to colorless, or anywhere in between.

If the do have copper, you heat them until the purple/red/brown has faded away entirely and you are left with the cyan color that the other colors have been masking. I am not sure that the color is changing during heat, but maybe only fading away to show the copper color.

Of course very rarely tourmaline can have that cyan color naturally with no trace of copper. Also, the cyan color can be found in tourmalines that are copper bearing and don't need to be heated.

So you see it is very complicated. I do know that from the African deposits I usually work with, purple stones that have copper become Paraiba color after heating. No copper in the stone, then no Paraiba color. So it seems copper must have a role in stones from these deposits.


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 Post subject: Re: The challenge of Paraiba rough
PostPosted: Mon Apr 06, 2020 6:46 pm 
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So if I understand all right, this kind of dark purple rough is only bought with the hope that after heating it will turn to a highly desired cyan blue color, thanks to the presence of copper ?
Would you have perhaps a picture showing the rough before/after treatment ?


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 Post subject: Re: The challenge of Paraiba rough
PostPosted: Mon Apr 06, 2020 7:08 pm 
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Isi wrote:
So if I understand all right, this kind of dark purple rough is only bought with the hope that after heating it will turn to a highly desired cyan blue color, thanks to the presence of copper ?
Would you have perhaps a picture showing the rough before/after treatment ?


The purple color without copper can be heated to lighten and brighten the color. This produces very attractive purple tourmaline that sells for a good price.

However, since the Africans assume all stones this color have copper they ask the astronomical Paraiba price for them. I have been able to test and buy non copper bearing purple tourmaline for about $50/gram. With copper the selling price is $500 - $2,000/gram depending on size and clarity.

The parcel I showed pictures of in this discussion has not been agreed on yet. The shutdown has made this impossible considering the mixed nature of the lot. The seller has asked me to hold it in my safe until the ability to travel returns when he will bring more and come out in person to hopefully finish the deal. So on this lot I cannot heat the stones.

Here is a nice study on the subject that shows stones of various colors and trace elements before and after heating. As you will see the spectra of the copper doesn't change during heating. It is the MN2 that changes, which I believe is responsible for the red/purple/brown and this changes during heating.



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 Post subject: Re: The challenge of Paraiba rough
PostPosted: Tue Apr 07, 2020 9:12 am 
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Very interesting. Thank you 1bwana1.
I love the polychrom cut stone shown in the article.
This tourmaline heating affair seems to be quite a russian roulette.
Either you get the desired blue color, or you are left with nice-looking but rather usual color tourmalines.
The purple stones look no better to me than amethysts or spinels, event though they can be called Paraibas.
Maybe they look different in real.


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 Post subject: Re: The challenge of Paraiba rough
PostPosted: Tue Apr 07, 2020 11:13 pm 
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Isi wrote:
The purple stones look no better to me than amethysts or spinels, event though they can be called Paraibas.
Maybe they look different in real.


They do look very different in person. The brilliancy and the glow is there : amethyst looks completely dull and "flat" next to them.


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 Post subject: Re: The challenge of Paraiba rough
PostPosted: Wed Apr 08, 2020 12:31 pm 
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Dioptase wrote:
Isi wrote:
The purple stones look no better to me than amethysts or spinels, event though they can be called Paraibas.
Maybe they look different in real.


They do look very different in person. The brilliancy and the glow is there : amethyst looks completely dull and "flat" next to them.



Yes, there is a neon character in all colors of copper bearing tourmalines that make them special and more attractive. Of course this shows best in the cyan to green color range. However, I never keep the purple ones purple. I always heat these to reveal the more desirable colors underneath.


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 Post subject: Re: The challenge of Paraiba rough
PostPosted: Wed Apr 08, 2020 1:39 pm 
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Quote:
Yes, there is a neon character in all colors of copper bearing tourmalines that make them special and more attractive.


I have a client who buys all tourmaline with lab reports indicating copper. Some ugly crap, I have to say. He buys cheap and presumes there will be a great profit to be made.

I think simply having trace amounts of copper present in a tourmaline xl, does not ensure a "neon glow"

I suspect that there may be a Copper flavored Kool-Aid which effects our ability to see drab, non-neon colors and tones. :wink:


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 Post subject: Re: The challenge of Paraiba rough
PostPosted: Wed Apr 08, 2020 6:09 pm 
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Barbra Voltaire, FGG wrote:
Quote:
Yes, there is a neon character in all colors of copper bearing tourmalines that make them special and more attractive.


I have a client who buys all tourmaline with lab reports indicating copper. Some ugly crap, I have to say. He buys cheap and presumes there will be a great profit to be made.

I think simply having trace amounts of copper present in a tourmaline xl, does not ensure a "neon glow"

I suspect that there may be a Copper flavored Kool-Aid which effects our ability to see drab, non-neon colors and tones. :wink:


Yes, there are some green/brown/yellow stones that have very poor color even though they have copper. Many people will also buy copper tourmaline that is so included they are only translucent, or have cracks that have been filled. The rules of stones should not change just because of copper. They should still be attractive to bring a decent price.


Last edited by 1bwana1 on Thu Apr 16, 2020 7:04 pm, edited 1 time in total.

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 Post subject: Re: The challenge of Paraiba rough
PostPosted: Wed Apr 08, 2020 6:21 pm 
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Bravo, Steve! That's what I'm talking about.


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