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GIA’s 73rd Gemstone Gathering


“Tanzanite: Facts, Fairytales and Fakes”


Jeffery Bergman
Director of Primagem

About Jeffery Bergman

Jeffery Bergman, an American gemstone dealer with 40 years experience in the mining, cutting, wholesaling and retailing of gemstones and fine jewelry is the Director and founder of Primagem based in Thailand. Cutting his first gemstone at the age of 14 started Jeffery on a 4 decade career that has taken him to over 50 countries and every continent except Antarctica. Jeffery has been featured in many gem and jewelry periodicals and has appeared in interviews on the BBC, CNN, NBC, ABC and GEO. He has also been quoted in Time, USA Today, National Geographic, Gems & Gemology, Discovery Channel magazine and many other publications around the world, and has been a guest speaker at gem lab seminars and gemological association conferences and universities.


Vivid blue zoisite was discovered near Mt Kilimanjaro in 1967. Thanks to the marketing prowess of Tiffany and Co. we all now know this rare gem as Tanzanite. Prized for its strong trichroism, exceptional clarity and generous sizes, Tanzanite is now found in jewelry stores worldwide and has become a household name.
This three-part presentation opens by exploring the history, geology and gemology of this popular gemstone. Next, gemological rumors of new treatments are examined followed by a review of Tanzanite imitations and how to detect them.


Jeffery Bergman returned to Thailand and GIA’s Gatherings events to give a presentation on the popular gemstone Tanzanite. The presentation itself was inspired by rumors in the market surrounding treatments applied to Tanzanite which needed to be addressed, and although Jeffery admits that tanzanite is not a gemstone he deals in, he took it upon himself to get to the bottom of the matter and reveal the truth as that is the way he thinks, and his business ethics dictate that the truth should be disclosed for the benefit of consumers and the trade. Since this matter arose early in the year he consulted with Hayley Henning of Tanzanite One to work on a presentation for the JCK show in Las Vegas. The result was the same presentation, bar a few minor edits, that Jeffery shared at this September Gathering. Jeffery also informed the attendees that he would be presenting the same work at a gemological event in Napoli the following weekend, and to GIA alumni in San Francisco in October.
In the way of an introduction, Jeffery said that he would break the presentation down into five separate parts and it seems fitting to do the same in this synopsis. Yet before he got down to the actual detail he was clear to state two important points. Firstly he does not work, nor ever has worked for the GIA and secondly, he has not been paid to produce the presentation.


The Merelani deposit with which Tanzanite is closely associated is located within the Mozambique Orogenic Belt where the extensive metamorphism that took place millions of years ago kindly provided the right elemental soup from which Tanzanite and other valuable gemstones formed in one of the planet’s richest gem source regions. This was clearly illustrated by Jeffery via a Richard Hughes related map that show Arusha, the town most closely linked to the Tanzanite source (close to Mount Kilimanjaro, Africa’s highest mountain), situated within a belt that contains the names of gemstones sources such as Winza, Umba, Morogoro, Voi, Mahenge, Tunduru and Songea, that are well known to anyone involved with gemstones and their sources. Tanzanite itself was found near Arusha in January 1967, and as the majority of people familiar with its history know was subsequently named Tanzanite by Tiffany & Co.
The crystal specimens of Tanzanite recovered are often associated with graphite, which is hardly surprising since the source is in the middle of one of the world’s largest graphite deposits. This point would become important later in the presentation so Jeffery asked the attendees to make note of it!
In the meantime Jeffery showed a whole series of slides that provided a wonderful overview of the mining operation itself at the Merelani mines, including images that showed the strict security in place in the sorting area where staff never actually touch the rough gems when recovering them from the ore or later in the sorting stage. These operations are all carried out via gloves that are affixed to sealed and windowed sorting stations, so there is no risk of theft. The only stage where the workers appear to touch the rough is of course when the Tanzanian workforce have to transform the stones into the faceted end product that reach the world’s markets. At this point Jeffery emphasized that the gems also come with certificates of authenticity that prove the ethical mining and handling of the stones as well as which prove that the local community is benefitting from the industry.


Tanzanite is a complex calcium aluminum silicate (sorosilicate) that is mineralogically referred to as zoisite in which the primary chromophore vanadium produces the coveted blue/violet coloration. Secondary chromophores of chromium, iron and manganese are responsible for pink, green and yellow stones. Jeffery also listed all the properties gemologists would use to help identify the real gems from their imitators, and specifically mentioned the hardness of 6.5 on Mohs scale, the birefringence and pleochroism as the most important of all the properties as a gemstone.


Everyone is aware that heat treatment is carried out Tanzanite and consequently the vast majority is treated at temperatures around 500 degrees Celsius, which removes the brown/yellow component leaving the more desirable blue/violet. Some labs state “No indications of treatment” on stones and some claim they can identify treatment in some stones with certainty. Exactly how accurate such claims are is open to debate, since Tanzanite is altered at low enough temperatures to also be affected by bush-fires, for example, which are not uncommon at the source of such stones. Thus proving exactly how they were heated, even if they are, is another matter altogether.
Another treatment that Jeffery touched upon was the coating applied to some stones that started to appear in the market around 2006. The very thin coatings were applied to the pavilion and girdle areas only and in some cases needed advanced testing to prove their treated nature.


This was the “fun” part of Jeffery’s presentation as he put it. The three main points he focused on were “diffusion treatment”, “dyefusion” (aka color infusion), and “irradiation + grain boundary diffusion”. All these “theories” were released upon the trade and consumers by an organization called The International School of Gemology (ISG) based in the USA. Yet, there is sufficient evidence to counter the claims and show that the statements are in fact more of a scaremongering process that needs addressing, hence Jeffery’s involvement in trying to show the facts through presentations such as this one. Jeffery even showed how the fear factor generated by such false claims lead others to pick-up on the claims and create their own websites and thus exacerbate the fear factor even further!
On the first of these subjects a post on the Gemology Online forum in January 2013 stated that the poster had heard of diffused zoisite (Tanzanite) hitting the market in Thailand in large quantities, at cheap prices and all of the same color. This was addressed when ISG sent numerous tanzanite samples suspected of being treated to Tanzanite One who in turn sent them to noted gemologist Christopher Smith of the American Gemological Laboratories (AGL) who subsequently stated that he had not seen any evidence of such a treatment in zoisite. This appeared to quash this rumor since little has been heard of the matter since.
The “dyefusion” matter however arose when claims by the ISG about the sudden increase in material of the same quality and color being atypical and due to treatment hit their website and associated industry forums. However the main question that arises from such a claim in the first place is “What increase in Tanzanite supplies?” According to Jeffery, who has extensive trade experience at shows in the USA, Europe and the Far East, there has been no evidence to support such a claim at all. The supply appears to be about the same as it always has been. To support this Jeffery dug a bit further and reproduced a chart showing the historical values of Tanzanite to see whether any such supply of “cheap” atypical Tanzanite had dramatically altered the market for the stones in recent years. He found some data courtesy of Gemval.com that showed prices did indeed peak around December 2012 and have recently started to decline a bit (a few percent) but Jeffery suspects this has more to do with the ISG scaremongering (given the timing of their publications) than anything to do with there being such material in the market.
With the latter in mind Jeffery set out to show the misconceptions in the arguments put forward by the ISG and began by explaining the ISG claim “4 colors – 2 natural – 2 due to treatment?” Using the section on Tanzanite in Antionette Matlin’s book “Gem Identification made easy” and  a standard Gem-A London dichroscope he showed that it is not unusual for Tanzanites that may be of a natural color to show at least three different colors including yellow which was shown in the example the ISG claimed to be “dyefused”. Another important point that the ISG used to “support” their argument was that melted metal found to be annealed pyrolitic graphite was observed on such supposedly color infused stones. Yet when one considers the graphite source, graphite is not a metal as ISG state but pure carbon, and Tanzanite’s association with this mineral as mentioned by Jeffery right at the beginning of his presentation the annealed graphite comes as no surprise since the annealing temperature of graphite is 250 degrees Celsius whilst zoisite undergoes dehydration melting at 780-820 degrees Celsius thus making the annealed graphite a likely occurrence on typical heat treated Tanzanite gems where graphite exists. This makes the ISG’s claim that melted graphite, graphite melts are 3650 degrees Celsius well past the dehydration melting of zoisite, a physycal impossibility.
Another piece of evidence the ISG used to support the claim that the material they studied was “dyfused” was the observation of “purple liquid material inside an internal tube”. Yet Jeffery tracked down an article by the Geological Society of Finland in 1986 that stated fluid inclusions exist in zoisite (Tanzanite), he also learnt that it is impossible to conclude such a substance is “foreign” without advanced testing which was never the case with the sample examined by ISG and lastly if such a material was identified as “foreign” after such testing it would be considered as just “dyed Tanzanite”.
This led Jeffery on to more examples of ISG claims in what he entitled “ISG/WGS Smoke and Mirrors”. The first dealt with a specimen that showed clear yellow coloration mixed with the typical variable blue/violet expected of Tanzanite. The text accompanying the sample stated that the yellow color “is obviously due to a foreign substance in the stone, we believe this is a flux material of some type. But broken into this area and along the predicted path of a fracture in the stone, you see the purple coloring material from the color infusion process.” and using simple diagrams with standard logic and photography of untreated (other than possible heat treatment) stones Jeffery was able to prove that the simple explanation was nothing more than reflection and the well-known property of pleochroism inherent in all Tanzanite! The purple coloring material referred to in the article is nothing more than the reflection of the natural purple color for which Tanzanite is so coveted. As one of Jeffery’s slides stated “Dyefused? Color Infused? Someone’s Confused!”
The last of the ISG claims, “Irradiation and Grain-Boundary Diffusion” came under scrutiny next when Jeffery quoted some more text from another of their articles which states “But we do have plausible information, as well as verification through specimens, that radiation plays a major role in the preparation of the gemstone crystal for the diffusion process.” The main concern here is that irradiation is said to be used, yet irradiation is used on gems to create defects, usually vacancies, in the lattice of the material under treatment rather than any channels along grain boundaries as implied in the text.
If we therefore make the huge assumption that such “channels” are created the size of the atoms being displaced and subsequently introduced need to be considered. In the case of the complex chemical formula of zoisite it would be fair to choose the largest of the atoms, which happens to be calcium as the one to displace. If the artificial dye indigo is then chosen as the replacement material the 30 atom molecule that comprises it would then need to be squeezed into the space once occupied by just the one calcium atom. This would be like squeezing a pumpkin through a wedding ring and the consequences would be just as messy!
IF, this miracle were ever accomplished though it would still not be considered diffusion or any of the other terms that the ISG would like the trade to believe, but simply dye once again. To sum this part of the presentation up Jeffery had a simple message to share with everyone concerned with Tanzanite treatments suggested by the ISG; “Have no fear. Such rumors are complete fairytales”!

Real Fakes

The final part of Jeffery’s presentation covered the actual stones that gemologists should have some concern about with regards to separating them from the real Tanzanite gems, namely the fakes that exist in the market. Firstly the important matter of synthetic zoisite was covered. At the current time crystals measuring only 0.03 mm have ever been produced, so as far as the gem industry is concerned there is no immediate or ongoing concern in this regard. Jeffery then went through a list of materials, with or without misleading trade names used to match Tanzanite better and thus provide a degree of confusion, such as synthetic forsterite, synthetic spinel, Coranite (synthetic sapphire), Tanavyte (Yttrium Aluminium Garnet), Tanzation (synthetic spinel/cobalt glass triplets) and synthetic cubic zirconia amongst others.
Whilst the list may appear alarming to the average gemologist student it is not as bad as it may first appear as most of the Tanzanite simulants react in some way to ultra-violet lighting whilst Tanzanite itself is inert. So this is one quick and easy test that helps greatly. Synthetic forsterite one of the main worries amongst gemologists at one time is both highly birefringent and reacts to UV light, so it is easily separated from Tanzanite with simple tests. In ending yet another highly educational and entertaining GIA Gemstone Gathering presentation Jeffery added that the use of the Hanneman Tanzanite Filter is, as would be expected, a very useful addition to any gemologist’s arsenal when it comes to simple tests available to help in the separation of Tanzanite and its simulants/fakes.