Truth in Tourmaline

Welcome Honored Guests

The Specialty Of The House Is Truth In Tourmaline

Exceptions And Comments Are Appreciated

Dark flash driven green emerald cut, usambala. 20 #4 This dark flash driven green emerald cut is a Dravite, the species, and displays the usambala effect. It appears to be eye clean and weighs 1.12 carats.

This is the tourmaline in my collection that I will use in the following discussion on this page.  It weighs 1.12 carats.

I would like to start this meal off with a color change delicacy.  For most of ten years I have been closely tracking color change in tourmaline.  It started when I discovered a new variety of Elbaite, (Lithia Tourmaline),  that I have since begun to call Laurellite.  It is an unheated cuprian tourmaline that demonstrates a reverse alexandrite color change from purple  in cooler natural light to blue/ blue green in warmer incandescent light. (There are more complete and detailed posts on this site, so I will move on with out regurgitating too much).

During my forays, to both find color change tourmaline on the inter net and read about them, I kept running into listings of different varieties of  tourmaline.  Many times there was a brief item that was only called color change tourmaline.  This variety, which is certainly not the only color change tourmaline out there, was said to be green in natural light and red in incandescent light.  Now I wanted some of this in the worst way, but I never saw anyone with rough or even a cut stone of this variety of tourmaline.  Not even a picture of one in a museum.  Wow,talk about scarce.

Finally I found one the other night on a site that I feel is both legitimate and knowledge.  It describe a dark, roughly one carat stone that went from yellowish-green in well balanced natural light to a reddish orange in incandescent.  The origin of the the rough material was given as the Umba river in Tanzania. Recently, I have continued to find indications that  a true red to green color color changer exist in tourmaline.  I am on the quest for one to test with my spectrometer.   It will have to be a different event than when I found an usabara tourmaline in my collection as I relate in the next paragraph.  

While I was obtaining absorption information, with my spectrometer, for all the tourmaline in my collection,  I found a green tourmaline that flashed red when I placed my high intensity fiber optic light source on them.  Now red flash from a green tourmaline is quite unusual to say the least.  (The red flash comes from the intense light being still visible after multiply reflections, that increases the light’s path length within the gemstone.)   I have since done a demonstration with a friend to show that I was seeing the usambara effect.  I placed my gemstone on top of her gemstone (table to table) and together they turn red, while each separate gemstone was too think/small to switch from their green color, alone.  The critical point for not being a color changer is that it was all done under only one light source.

 

Bruce

 

Next on the menu is precious dish.

 Paraiba Tourmaline and Gold

Even before copper was discovered in gemstones I supplied the GIA in an effort to understand why the material I had obtained from Mozambique had a reverse alexandrite color change (see Laurellite posts), I was very interested in the causes of color in Paraiba tourmaline.  I was relatively new to the inter net and I was surprised to read over and over again that a study by the German Foundation for Gemstone Research had found levels of gold in Paraiba that were higher than the average concentration found in the earth.  I also wonder why this bit of information merited such importance.   Yes, it would set Paraiba tourmaline apart from other tourmaline, but would physically have no effect on its color or any other significant physical attribute at the levels found.  This is not unique to tourmaline, but is a fundamental property of the electronic configuration of gold.  So when I began to read a mutation on the original report of high levels of gold in Paraiba tourmaline, that stated that gold helped color tourmaline, I had to dig deeper.

The first thing I tried was to contact the German Foundation for Gemstone Research.  I was very surprised to get an immediate responce that was an indignate question.  Who is reporting that?  It was obvious that they did not support the report.  But I needed more support to understand where the gold in Paraiba report came from.  I read two of the original papers on color in Paraiba tourmaline.  An American paper that states gold had been reported to have been found in Paraiba by A group of German researches, but could not verify it.  I then read the German paper, that was based on one piece of Paraiba tourmaline and found no report of gold in there sample of Paraiba tourmaline.

Now why a ground breaking, highly influential, research report would mention the report of gold in Paraiba tourmaline without verifying it and my interest Laurellite (a variety of cuprian Elbaite) lead me to investigate the testing of tourmaline for trace elements.  Tourmaline is very difficult to test with traditional methods because it is for all practical purposes, completely insoluble in acids at  standard temperature and pressures.  This has lead to two methods of preparing tourmaline for analysis.  One is the fusing of the tourmaline with a flux.  The combination can then be dissolved in acid and analyzed.  the second method uses a Teflon bomb and hydrofluoric acid.  The tourmaline and acid is heated in the bomb to high temperatures by a microwave furnace.  After striping out the fluoride ions, the tourmaline solution is analyzed.  Both of these methods have problems with contamination in either the flux or acid and certainly are expensive to do with the many careful steps that need to be performed.

More direct methods of analysis have been developed over the years.  The use of xrays can now be used without the need of for disolving the tourmaline to analyze for all concentration of elements in tourmaline if the properly calibrated canals have been set up.  This method and others are beginning to take a back seat to a relatively new kid on the block.  It is called LA-ICP-MS. which stands for Laser Ablation Induction Coupled Mass Spectrometer.  This method permits the formation of a charged gas that can be separated by a   different electrical attraction for each ion, into it individual elements.   This method of analysis has its calibration problems as well, but when done well, it gives quantitative data on most elements in the periodic tables.  The exclusivity of the testing is important, along with its accuracy in measuring of very low levels of the trace elements because you find out information on elements you may have not expected to find or have interest in and therefor not set up to analyze for them.

Since the time frame that would have covered the reporting of the gold in Paraiba tourmaline and the two early papers on color in Paraiba tourmaline, a large number of LA-ICP-MA tests have been performed on cuprian tourmaline.  I use the generic nomenclature here because Paraiba tourmaline is only a small subset of the tourmaline that is copper bearing.  This testing has been preformed, in part to build libraries of data sets to distinguish Paraiba tourmaline from Paraiba like tourmaline from Mozambique and Nigeria.  In all this testing with an advance method that is extremely good at preventing contamination, no level of gold has been reported in any cuprian tourmaline, which of course includes Paraiba.  Any clear unequivocal difference that Paraiba tourmaline may have from the rest of the cuprian tourmaline world , and there are subtle differences, would have been loudly reported because literally millions of dollars have been spent looking that very key to keeping Paraiba tourmaline more highly valued and distinguishable, even in lower grades of material.

So to sum up.  The German foundation that was reported to have found gold in Paraiba denies it.  The only scientific paper that I can find and I have looked with help from a friend in academia, makes only a unverfied reference to finding gold in Paraiba while the final referenced report does not included anything about gold in Paraiba.  This early work has been followed up with a massive amount of highly accurate inclusive testing of all sources of cuprian tourmaline including Paraiba without one single report of gold in the tourmaline samples tested.  And gold could not influence color even if it was present based on universal physical laws.  No gold in Paraiba, Truth in Tourmaline!

A final personal observation.  I am cynical of much of the trades promotions, but when it comes to high quality copper bearing tourmaline, its beauty speaks louder than anything they have come up with.  Unfortunately color is not the key and that will be the next installment on Truth in Tourmaline.

Bruce

Cyan color, Paraiba, paraiba like, paraiba type and the neon glow.

When Paraiba from Brazil first hit the market in the late 1980s and was accepted as a natural beauty, many attempts were made to stretch English to express the wonderment of its beauty.  Its hue/color was compared to Windex blue, electric blue etc. and its visual impact as vivid, neon, etc.  With the advent of the discovery of paraiba like (cuprian) tourmaline in Nigeria, the chorus became even louder because now the trade had more material to invest their effort in.  Finally the much larger deposit of paraiba like tourmaline from Mozambique, with its larger clean gemstones has helped put this variety of tourmaline into the stratosphere.  Along the way to this pinnacle of promoting there have been many disappointments. (one of the reasons I did not send in samples of tourmaline from Mozambique, that turned out to be cuprian, earlier,was the numerous disappointments in finding new deposits of paraiba like tourmaline)   The biggest and most important failure, was not finding copper in tourmaline from Afghanistan/Pakistan.  Stories circulated about special agents scouring the countryside and paying exorbitant prices for the individual pieces of precious rough.  Dealers with many years of experience waited with bated breath, to get analytical reports back from the worlds best gemological laboratories, to confirm the magic of copper.  Then the euphoria and hype hit the wall of negative reports, the beautiful cyan blue tourmaline from Afghanistan/Pakistan did not have copper, it was colored by lowly iron.  Prices that were reaching for the sky, moderated and very little has been heard about the material since.  (I was actively buying rough from Afghanistan at the time and my principle dealer promised me that if I visited him in California, he would let me hold his piece of paraiba from Afghanistan/Pakistan.  By the time I got there the wave was past and we talked of other things.)

At about the same time I had made contact with a high end gemstone dealer in Kentucky.  I wanted to get acquainted with him and show him my collection.  It was while I was visiting him, that I first saw high quality emerald cuts made from the cyan colored, want to be copper bearing, tourmalines from Afghanistan/Pakistan.  They are impressive, but something is lacking.  I have since made another trip to visit him and brought my new spectrometer with me, to check out a couple pieces of unheated Paraiba tourmaline from the original pocket that are still in the rough state.  He was interested in having only one type of gemstone tested for himself,  The cyan emerald cuts from Afghanistan/Pakistan.  He said his customers just can not believe that they do not contain copper.  Well my spectrometer verified that they do not contain copper.  So what is going on and what is missing, when they have the identical color of some high grade copper bearing tourmaline?

The gemstones are bright, but they do not have the same high level of  neon glow found in the best  copper bearing tourmaline.  When I include the neon glow along with the cyan color, into the visual presence of the gemstone,  I feel that cuprian/copper bearing/paraiba-like/Paraiba is more exceptional than the iron based cyan colored gemstones.  I say best copper bearing tourmaline, because the neon property does vary in my collection of copper bearing tourmaline from Mozambique along with sea foam from Afghanistan/Pakistan.  I have also found that I have a similar non copper bearing cyan stone in the collection that has a very good  color, but not a high level of visual presence, when compared with top quality copper bearing tourmaline.

So what is the bottom line here.  Cyan is a beautiful color anywhere it is found in gemstones.  The presences of copper in tourmaline does not guarantee that the gemstone will have a neon glow about it.  Without a superior neon glow, cyan copper based tourmaline is not intrinsically superior to cyan iron based tourmaline.  What causes the neon nature of a color to be expressed, is a good question.  I think that is revolves around the level of the spectral purity of the stone’s color and its perceived brightness.

I have limited the discussion to cyan blue because it is the color that is most desired in copper based tourmaline and I can compare it with cyan, iron based tourmaline.  But I definitely see indications of copper, as a chromophore, in other bright colors of tourmaline.  Whether these other colors have more or less of the neon glow, than similar colors produced by other chromophores, I am not prepared to say.  Maybe I will have more information when I get my upgraded spectrometer operational.

Reverse Alexanderite Color Change Gemstone, Cuprian Tourmaline from Mozambique,  Laurellite.

In this post I will limit myself to a simple truth that has not been picked up by the internet and how it continues to propagate an older theory of color change that CAN NOT BE TRUE.  I will not write about the proposed theory of why color change occurs in gemstones, because it still controversial, I expect, or at least not generally accepted.  Also the new theory will be more fully dealt with in other posts.

The older theory that is universally propagated on the inter net (at least as far as I can tell) is simple and straight forward.  You take a gemstone that has at least two different transmission peaks in the visible light range and two”white” lights, in particular natural light and incandescent light, with different ratios of red/blue light.  If the ranges of visible light transmission peaks are appropriate for a different color to completely dominate the gemstone under each of the two different “white lights”, it is called a color changer.  The change is always to a warmer/redder color under incandescent/artificial light because it has much more red in it than natural light and cooler/bluer color under natural light because of its bluer nature.

When I first discovered the reverse alexandrite color change effect in a gemstone I cut from cuprian (I did not know it contained copper at the time) tourmaline, I obtained from Mozambique, I was amazed.  I had never read or seen anything about such a color change.  I did not realized until after the color change was verified by the Gem Institute of America and further color studies were run by an independent expert that this reverse alexandrite color changer was a “smoking gun”.  By “smoking gun” I mean that Laurellite’s (a name I have given the new variety of Elbaite tourmaline) color change from a purple (warmer color) in natural light to a blue (cooler color) in incandescent light has killed the older simple model of color change in not just gemstone, but all materials.  No matter how perfectly the old model/theory of color change seems to explain the colors of ruby, alexandrite and emerald, (The universally used examples of color production and color change in gemstones.),  IT CAN NOT BE THE COMPLETE TRUTH.

Bruce

Pleochroism,  Dichroism and  Tourmaline.

Tourmaline is not the most dichroic gemstone of all gemstones or in fact intrinsically dichroic at all.  I prefer to use dichroic rather than pleochroic because tourmaline can only express two colors in a crystal that are based on different axis of the crystal.  I prefer to use pleochric for crystal that show different colors on all three axis like unheated Tanzanite.

All four mineral species, that are usually cut into gemstones, in the closely related group of minerals that mineralogist and gemologist call tourmaline, are intrinsically colorless and therefor not dichroic.  These four minerals species are Elbaite, Liddicoatite, Dravite and Uvite, can not be distinguished by color or any other physical feature without appropriate testing equipment.

The level of dichroism that can be expressed in Elbaite, by far the most common mineral species used in gemstones that are referred to as tourmaline, can be from no absorption to complete absorption down the principle axis. (c axis).  When the principle axis is in essences opaque in tourmaline the common way of saying that is,  the tourmaline has closed ends.   The most interesting feature of dichroism in tourmaline is not the spread of absorption between a colorless (achroite) and lets say a dark blue indicolite, but the tremendous difference between dichroic and non dichroic indicolite (other colors too) at all tone levels.  This dichotomy, between non dichroic and dichroic tourmaline with the same color and tone level is important for both the cutting of a gemstone and identifying cut tourmaline.  One aside should be made here, if the tourmaline is dichroic, the principle axis, (c axis) will be darker than the a/b axis.  I use the designation of a/b axis as one axis because these axis must be the same color, because of the geometry of the tourmaline crystals.

So the mystery grows.  How can an intrinsically non dichroic substance, show a complete range of dichroism, that is independent of the both the color and tone level of most tourmaline.  The secret lies in the form of the chromophore that is incorporated into the tourmaline crystal.  A chromophore is unusually a transitional element or combination of transitional elements that has the proper electronic configuration to absorb visible light and cause color in a substance.  If the chromophore is in the form of an intervalence charge transfer, (IVCT), the internal structure of the tourmaline will alignment the axis of the IVCT  with the c axis.  An IVCT requires two atoms that interact to absorb visible light.  The axis of the  IVCT is a much more potent absorber of visible light than its other orientations.

Well there you have it.  The wonderfully complex electronic nature of tourmaline is ready to orient some coloring agents that are strongly dichroic (IVCT) with its principle axis while other coloring agents are not imparted with any preferential absorption orientation, which results in beautifully open ended tourmaline.

I do have one unanswered question about the orientation of IVCT in tourmaline and that is whether all IVCT are aligned in all tourmaline under all conditions of growth.  I do know that some tourmaline can have their axis of darkness not be aligned with the terminus of their crystals.

CHEMISTRY, COLOR, CANARY TOURMALINE, ELBAITE TOURMALINE

The choice of what to write on this page finds it roots in surfing the internet.  There are many parts of the saga of tourmaline that I could not care less about, whether they are true or not.  My indifference to tourmaline’s mystic and health issues keeps me from endless reading exact duplicates of pages, on numerous sites.  But when it comes to color issues and chemistry, the endless repetition of statements present as the truth, when it is physically impossible, really gets me going.  I have picked two examples of what gets me going, in regards to tourmaline.

Lithium is an essential element in elbaite, an important member of the group of closely related naturally occurring chemicals (minerals) call tourmaline in gemology and mineralogy.  Essential means just that, you can not have elbaite without lithium, by definition.   Also the vast majority of tourmalines that are cut into gemstones are elbaite.   This is being clearly supported by a slew of modern, powerful, analytical methods.  So what am I building up to.  Pure elbaite is colorless and since lithium is an essential element in elbaite, lithium can not color elbaite.  Also, any reasonably competent chemist or chemistry book would have the knowledge, based on fundamental chemical principles, that lithium can not be a chromophore in tourmaline, period.  (in anything period)

I have not found the alleged coloring of elbaite by lithium on the inter net very much, but when I was in high school (1965 or so) I thought I was both pretty good in chemistry and gemology.  But I freely passed on, what I had read in my sources of knowledge about gemstones, that lithium made tourmaline pink.  I never did my homework until years later.

Now an analogous situation that has arisen more recently, because the importance’s of yellow tourmaline in the trade, is a relatively recent event.   I had purchased yellow tourmaline rough from East Africa long before “canary” was discovered, but there never has been much of the wonderful, pure, bright yellow color in tourmaline around.  I bring this up because without an economically important amount of a gemstone,  there is little incentive to promote  it or to write about it for the general public.  Without the public’s interest and the need for the trade to develop more interest, the endless echos of one “authority’s” mistake do not blight the inter net.

I think the mistake started when a well known and respected color gemstone organization set out to tell the public everything about colored gemstones on the internet.  In the case of yellow tourmaline, the only really important assertion that is made in the brief piece, is about traces of magnesium coloring tourmaline, yellow.  Now magnesium is not essential to elbaite (dravite is the tourmaline with essential magnesium and it is also colorless when pure), but the element can not be a chromophore in tourmaline or anything else for that matter, based on its electronic configuration.  Now I could go into unpaired electrons and transition elements with unfilled shells along with quantum mechanics, but I would just be trying to do the work that any decent chemistry books has refined to an art form.  Check it out and be freed from the echos of one writer’s mistake.

ELBAITE, LITHIA TOURMALINE AND ITS “DISCOVERY.

Well I found an internet page that actually had an original learning paragraph on Elbaite.  It was so original that it got almost everything wrong.  Most of the missed points I have gone over at least one time on these pages and I am not going to carry on about them again, but the humdinger that I want to talk about here is the declaration that the hitherto unknown subspecies Elbaite was discover on the island of Elba in the early 20th century. This is a prime example of someone who has read a little about tourmaline without any depth of understanding.

Lithia tourmaline was described for science based on the examination of material from a location on the island of Elba many years after it was well known in Europe.  One reason for the late date for the description of Elbaite is that Europe is very poor in suitable locations for finding Elbaite where it has been formed in the rock.   Also material from Ceylon and the east, where Elbaite is found in some abundance, was most  probably alluvial in nature or at least from deposits that were not accessible to scientist that were capable of describing the origin of the mineral.

Finally even the name “Elbaite” is a late bloomer that was introduced into the literature in the 1960s and did not come to be preferred over Lithia tourmaline until much later.

Bruce

COPPER DIFFUSION IN TOURMALINE

Copper is not a common chromophore in gemstones.  A chromophore is some impurity or imperfection that causes the gemstone to have color.  With the discovery that naturally occurring feldspar can be enhance threw the diffusion of copper into its matrix, it followed for some people, to think that tourmaline would be treated in the same way.  It certainly would have a significant effect on both the color of the material and its value.  And the added value would be greatly enhanced if the processing of tourmaline was kept secret.

What followed from the speculation about the diffusion of copper into tourmaline was an announcement that treated tourmaline had been found on the market.  And not only was it available, large amounts of the material had been secretively produced.   To support this contention a series of pictures with descriptions tried to convey the unusual nature of cuprian material that had been purchased on the open market.  Some provocative physical measurements were made of supposedly treat material and a promise was made to vigorously pursue the truth.  Other authorities in the gem trade took exception to the contentions about copper diffusion in tourmaline, that centered on the large differences in physical properties between feldspar and tourmaline and alternate explanations for the unusual nature of cuprian tourmaline rough.  Even the GIA, Gem Institute of American started testing samples of tourmaline for signs of treatment and the practicality of treatment.

I had personally observed a halo of purple around inclusions in a cuprian tourmaline that was mostly blue from Mozambique long before any concerns about copper diffusion had be put forward.  To me from the beginning it was obvious that impurities in the inclusion had been radioactive and oxidized the Mn2+ to Mn+3 and causing a red hue that modified the underlying blue color to purple.  And most important of all, I knew that rough, that I had gotten directly from Africa, had not been treated in any way.

Based on personal observations and my back ground in chemistry I strongly doubted the diffusion of copper into tourmaline as a chromophore.  Questions about the thermal stability of tourmaline at standard temperature and pressure along with the lack of suitable diffusion paths in the crystal structure of tourmaline supported my contention.   Other technical points were made by knowledgeable researchers and the contention that any amounts of diffusion treated tourmaline were available fell apart.  I don’t think that the testing being done by the GIA was even completed.

As a adjunct to the diffusion of copper in tourmaline was the contention that synthetic tourmaline was available commercially.  This was also successfully disputed to the point, where I am confident that no synthetic is available on the commercial market and no tourmaline of any kind has been successfully diffused with enough copper to affect its color.

Bruce

 

 

 

 

 

Bruce

Leave a Reply