CIBJO releases Gemmological Special Report: considers process of separating measurable facts from opinion; See Gemological Articles below.
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 Post subject: Beautiful tourmaline, GIA educating the public?
PostPosted: Sat Jun 22, 2019 9:16 am 
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Ah, a video on youtube by the GIA called Beautiful Tourmaline. Now that sounds interesting, but then it is only 57 seconds long. Wow, I am impressed as I lay back in bed convalescing from hurting my foot, by the rapid fire slide show of exceptional tourmaline that must follow. In less than a minute later, I was proven wrong in a totally unexpected way.

The "Beauty of Tourmaline" turn out to be an attempt to explain difficulties in naming tourmaline due to its complex nature. The only snippet that came off wrong to me was a one line definition of chrome tourmaline. The essential fact that chrome tourmaline might really be colored by vanadium and not chrome is presented clearly enough, but the use of "intense green" to describe its appearance left me wondering.

What does "intense green" in the description of gemstones really mean? Does that mean its green hue is without a modifier? Its tone level within a narrow band of darkness? And having a completely pure saturated hue? As you might have guessed I have my own opinions on the visual properties of chrome tourmaline and how closely Elbaite colored by iron can duplicate its "intense green". I am not the only one who questions the beauty of chrome tourmaline in all its range of properties. The high appraised value placed on brownish yellowish green tourmaline, that is colored by chrome/vanadium was roundly rejected in discussions in a recent set of posts. (I can easily see the difference between iron colored tourmaline and chrome tourmaline with my spectrometer.)

Now trying to leave no stone unturned, I decided to look for chrome tourmaline on youtube, that had a GIA report on a pictured chrome tourmaline. They were not hard to find. Vendors are thrilled to go threw the whole nine yards about chrome tourmaline's, with rarity leading the way.
The pictured tourmaline were far from intense green by any definition I care to support and without the lab work, I would say the gems were a pretty common yellowish green color with maybe even a brownish modifier. Certainly nothing to write home about.

So the instrumental methods of the gem labs has won the day again, just like with low grade cuprian tourmaline (sometimes called Paraiba). Disregard your eyes and go for the gold revealed by science. Oh and by the way, Paraiba tourmaline is never mentioned in the whole 57 seconds of the video the GIA has presented as "Beautiful Tourmaline". Every second is just too precious to waste on a subject that might demand the doubling of the length of the video to get it right.

Now I wondered about being negative with a sincere effort to educate the public about beautiful tourmaline. I should give world class organizations a break, when their public presenters drop the ball. So I went back on youtube, because I have been told this is where you find the truth! It took minutes to find a GIA video called "The Varieties of Alexandrite." Well, well that is a new one on me. Another gem lab chemical distinction that the eye has missed for so many years? The video was short again and dealt with the varieties of chrysoberyl not alexandrite. Alexandrite did get a brief description as chrysoberyl's most famous variety. I actually cut chrysoberyl in my distant past and I am glade I don't have to change my feelings about this beautiful gemstone with an unfortunate limit on its color spectrum. OK, OK, the miss labeling of the video was just a simple oversight, it really doesn't matter, the public will get it right in the end!

Bruce


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 Post subject: Re: Beautiful tourmaline, GIA educating the public?
PostPosted: Sat Jun 22, 2019 12:05 pm 
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I thought of GemeWizard because the term "intense" is used in their system of color descriptions.

What do you think of this YouTube video?


Also is everyone aware of this resource?
http://m.gemewizard.com/gemstones_colors.php


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 Post subject: Re: Beautiful tourmaline, GIA educating the public?
PostPosted: Sat Jun 22, 2019 8:23 pm 
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Thank you for posting the video, I had not seen it. It is much better than the GIA effort and closely follows most of the generally accepted statements about tourmaline. And they do make an effort to show you what they consider "intensely" colored tourmaline. But I take exception or have additions to some of the generally accepted statements about tourmaline the video has gathered together.

1, By focusing on the range of colors that partially define Paraiba and not discussing paraiba like tourmaline the video has not addressed an important issue in tourmaline. If all paraiba tourmaline had a strong intense color that iron could not duplicated, why did the Harmonization group come up with a new variety of tourmaline called paraiba like? Compounding the focus on the color range of paraiba tourmaline is the lack of any discussion of paraiba and paraiba like tourmaline's neon/electric/glow-like property that transcends any level of intensity/vividness/saturation in other colors of tourmaline. I have heard of dealers calling paraiba like tourmaline, indicolite with paraiba qualities and seen iron colored tourmaline from Pakistan/Afghanistan that has better glow-like qualities than copper bearing tourmaline that is called paraiba by the trade. It is a tough thing to resolve, but it should be addressed.

2, Tourmaline can not be pleochroic because of its crystal structure. The A/B axis of tourmaline must have identical colors and intensities. While the principle axis C must be darker than A/B if it is different than the A/B axis. In other words tourmaline can only have two colors that are dependent on viewing axis and it does not have to be dichroic. The degree of dichroism depends on the interaction of the chromophores in the tourmaline and the tourmaline's structure and is NOT an intrinsic property of tourmaline. I have many tourmaline gemstones in my collection that are not dichroic. This does not mean that tourmaline can not have many areas of color and color blending it a single gemstone. It excels at that, but if you cut out the individual color areas, the resulting stones would have at most two colors. ( I suspect that the definition of pleochroic is two or more colors depending on the viewing axis and is really applicable to tourmaline, but I think its use is deceptive since only two colors are possible and therefor dichroic is more appropriate.)

3, The discussion of golden tourmaline is interesting. The video talks about golden tourmaline colored by chrome, but it produces a different color than the green color of chrome in other tourmaline. I have tracked the progression of the change in color cause by the reduction in the height of the chrome absorption peak while, what I consider the manganese two peak remains unchanged, with my spectrometer. The lowest level of chrome peak I can see in the progression, produces a color change tourmaline that goes from brownish straw to yellowish green. In pure golden tourmaline I can not detect a chrome peak that is distinct from indications of iron. But since I can not afford to chemically analyse every tourmaline, I would like to, I only have the spectrometer data to speculate with. As far as "canary" tourmaline I think the video should discuss how it is colored since the new varietal name is brought up. (I never realized that Nigeria produce "canary" tourmaline.) In conclusion I have pastel yellow tourmaline gems that do not have the vivid color and tone values of canary tourmaline, and I think are colored by radiation induce color centers. They just do not fit in with the video's presentation or most other sources of information about color in tourmaline..

4, They must have almost run out of tape or just had a last minute thought when they included color changers. But then they are rare and so no one really cares about them. I personally would love to hear what they had to say.

So there you have my off the top of my head thoughts on additions to a fine effort to present the complex world of tourmaline in a short video. A video that needs some technical background to understand, but does not present anything of importance wrong. A most refreshing trip in my opinion as is every thing else in this post..

Bruce


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 Post subject: Re: Beautiful tourmaline, GIA educating the public?
PostPosted: Sat Jun 22, 2019 9:08 pm 
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I have always found everyone at GemeWizard more than willing to answer any question you might pose to them.
Menahem Sevdermish is a wealth of information and he is always willing to share.


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 Post subject: Re: Beautiful tourmaline, GIA educating the public?
PostPosted: Sun Jun 23, 2019 2:29 pm 
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A talk about everything to do with tourmaline would certainly take a lot longer than the video, but I found it generally sound. I hoped they would mention trapiche tourmalines, but of course there are so many subjects about tourmaline that could have been mentioned - treatments, reverse watermelon, closed C axis, etc..


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 Post subject: Re: Beautiful tourmaline, GIA educating the public?
PostPosted: Sun Jun 23, 2019 3:59 pm 
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Pleochroic is a general term that includes dichroic stones. Actaully I Personally kind of prefer that they avoid 'dichroic' anyway, since the term is also used to describe completely different phenomena (ie, 'dichroic glass').

(Side-note, tourmaline doesn't have a 'b' axis, just three identical 'a's, a1, a2 and a3).

It's not surprising they wouldn't address this extra 'glow' factor in paraiba tourmaline. It seems to be fairly hard to nail down in any quantitative sense, and they are in the business of quantifying color. Then again, if anyone could quantify it it should be them I guess.

I do think you should get in touch with them. It's hard to imagine that anyone else is as laser-focused on tourmaline color as you, and that should be of interest to them.

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 Post subject: Re: Beautiful tourmaline, GIA educating the public?
PostPosted: Sun Jun 23, 2019 9:24 pm 
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You have mentioned the major problem with grading paraiba tourmaline, the glow like factor. I do not know of any attempt to correlate the effect and the chemistry of the tourmaline This includes the level of copper. The reason as you presented it, is that it can not be measured by machine It is not a solely paraiba problem because sea foam colored by iron also varies greatly in its glow like quality. And it is important to the value of the gemstone.

I guess when it comes to naming axis in crystals it depends on from where your roots are. I have read many papers on crystal systems that use my terminology and never yours. It would be nice if the whole world marched together. I am probably dated.

The important point with different colors, when viewed from different axis is that tourmaline does not have that intrinsic property. You can not use it to identify all tourmaline. The best I can tell is most of my cuprian tourmaline have little or no change in color from a change in the viewing angle.

I have posted about where I speculate the yellow vector in tourmaline and paraiba in particular comes from. I have asked many times where the green (blue +yellow) comes from in paraiba/cuprian tourmaline. I am tired of coming out of nowhere and asking the question. t I have never received a complete and convincing answer based on the data we have today and not on old guesses. If someone out there has a personal connection with the person Barbra has said answers her questions, please communicate and ask him a simple question. What are the factors that make cuprian tourmaline green. If he responds, please post it on GO. I would greatly appreciate it. My focus is with the GIA where I do get some support.

Bruce


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 Post subject: Re: Beautiful tourmaline, GIA educating the public?
PostPosted: Mon Jun 24, 2019 12:39 am 
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I would define the "glow" you describe as intensity or saturation.
Intensity, as defined in color science, refers to the brightness, purity and vividness of a color.

I was taught that a trigonal crystal system would be labeled like this. I think we can credit Dana's System of Mineralogy, mid 1800s.
Image

Tourmaline, with the exception of achroite, is decidedly pleochroic. It's a diagnostic characteristic, no? C axis and a axis are typically dichroic.


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 Post subject: Re: Beautiful tourmaline, GIA educating the public?
PostPosted: Mon Jun 24, 2019 8:06 am 
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Thanks for the diagram and nomenclature on tourmaline's axis.

I can not agree with all tourmaline being decidedly pleochroic except for achroite. I have examples of tourmaline gemstones that prove to me the the eye can not see any color difference with viewing angle or any other indications of the c axis being different than any other axis in some colored tourmaline.

This whole area of dichroism for me goes back about 12 years ago when I was working with Rossman on the reverse alexandrite color changer I have come to call Laurellite. He wanted rough that had indications of the c axis, like striations or crystal faces. He could not orient the tourmaline visually. The explanation I have presented about the interaction of chromophores and the tourmaline structure is his explanation to me. He used charge coupled chromophores that are highly asymmetrical in their effect on color as an example of the interaction of the structure of tourmaline and a chromophore, that produces dichroism. If the chromophore was not asymmetrical the effect on the color of the tourmaline would be unaffected by its structure orienting the chromophore.

Lets move to a year and a half ago when I visited the GIA lab in San Diego. I had donated cuprian rough, to be oriented by a recently developed machine. (I was informed that Rossman has an identical machine now.) After orientation the material would be sacrificed by grinding it into a sample that had its faces perpendicular to the tourmaline's axis. Then the samples would be analysed. I have been recently reassured that the work will be published and I eagerly await that.

To sum up.

1, I have tourmaline gems that are not dichroic by eye. (I find blue to be a particularly interesting color in this regard. The difference between paler non-dichroic blue is so different from the more highly toned, strongly dichroic indicolites that perhaps a different name should be thought of. Thinking about it, maybe paraiba-like should have a more inclusive definition than tourmaline that looks like Paraiba, but is not colored by copper. I am going with the color, not the glow-like qualities, here.)

2, It is obvious that equipment can orient the tourmaline crystal when it can not be done by eye. I have seen absorption curves generated by spectrometers that are different, depending on the axis, even when I can not detect a visible dichroic effect. I don't remember the details of how the modern equipment at the GIA lab oriented my donated samples, but I expect the details to be in the research paper.

3, I find it interesting that I have never seen a paper on the explanation of dichroism in tourmaline that was privately presented to me by Rossman. Why don't you ask him what is up. I would be greatly interested in his latest thoughts and if I have missed something.

4, I will give you a couple of my most extreme example of a large non dichroic tourmaline in my collection.
One is a pastel green round that weighs 14.37 carats. Its number is 936 on my site brucefrytourmaline.com.

The other one is a pastel peach colored oval with a weight of 20.17 carats that has the number 500 on my site.
Image

I appreciate the desire for pictures, they are described and each have a picture on my site, but there is no way that I can demonstrate their lack of a visible dichroic nature with my photograph skills. Again the eye is essential to appreciating the intimate nature of the complex beauty of tourmaline. As an aside they both look like varieties of beryl, but I am sure they are not since my procedures to polish tourmaline tear beryl apart.

Bruce
Edit: Direct links supplied by admin.


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 Post subject: Re: Beautiful tourmaline, GIA educating the public?
PostPosted: Mon Jun 24, 2019 1:36 pm 
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Hi Bruce.
I think a lot of your questions were addressed in this early article describing Paraiba tourmaline. I'm sure you have read it before, but many of us have not.
Direct link:
https://www.gia.edu/doc/Gem-Quality-Cup ... Brazil.pdf


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 Post subject: Re: Beautiful tourmaline, GIA educating the public?
PostPosted: Mon Jun 24, 2019 6:25 pm 
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A polariscope should allow relatively easy determination of tourmaline's c axis. Similarly a dichroscope allows you to conveniently separate both colors side by side.

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 Post subject: Re: Beautiful tourmaline, GIA educating the public?
PostPosted: Mon Jun 24, 2019 8:25 pm 
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Of course, Stephen is correct.
A polariscope and coniscope can easily determine the c axis in tourmaline...even if it is a weather worn pebble.

Have you looked at your stones with a dichroscope, Bruce? I think you would find them both to be pleochroic.


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 Post subject: Re: Beautiful tourmaline, GIA educating the public?
PostPosted: Sun Jun 30, 2019 4:22 am 
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Bruce: "I can easily see the difference between iron colored tourmaline and chrome tourmaline with my spectrometer."

Me: I can easily see the difference between iron colored tourmaline and chrome tourmaline with my Chelsea filter.


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 Post subject: Re: Beautiful tourmaline, GIA educating the public?
PostPosted: Sun Jun 30, 2019 9:28 am 
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Thank you for your post. I would like to add a bit.

My principle connection for rough out of Africa some years ago had high quality chrome tourmaline.
The material he was selling showed red in the filter and was much more expensive than material that visually looked identical, but did not show red. I wish that I had been able to test the material that did not show red in the filter, he did not buy any, I am sure that I could see if it was colored by iron or maybe only by vanadium.

Again some years ago, I was talking to a mine that produced tsavorite and found tourmaline occasionally. The tourmaline would be green and they would judge it visually, whether it had the right degree of saturation/tone/hue to be chrome. ( the mine is in metamorphic rock so Elbaite would not be found.) He remembered one example that they ended up selling as non chrome. Later when he went to a European gem show he saw the same gem being sold as chrome tourmaline.

Tourmaline is complex and the buyer should be beware.

Bruce


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