AGTA GTC Laboratory Update
Feb. 27, 2007
In this message
- Pondering Paraíba Tourmaline
- FTIR Intrigue
- The Smithsonian Institution at AGTA GemFair™ Tucson
- Bulk Testing
- Upcoming Lectures
Current turnaround time at the AGTA GTC 5–7 Business Days |
Pondering ParaÍba Tourmaline
A major item of controversy in the gem world over the past year has been the definition of paraíba tourmaline. When this gem variety was first discovered in Brazil, the unusually intense "neon" or "electric" colors set it apart from any other tourmaline previously known. The color of this gem ranges from intense emerald green through "windex" blue-green to a rich sapphire blue and continuing along the spectrum to intense violet or even purple (similar to fine amethyst). Apart from the intense colors, another remarkable feature of these gems is their relative lack of extinction.
The above photograph shows a portion (blue-green to blue) of the intense color range typical of paraíba tourmaline from Brazil. Photo: Wimon Manorotkul/Palagems.com |
Because the colors were so unusual, traders immediately began marketing the gems under the moniker "paraíba" tourmaline, after the Brazilian state where they were first found. Later, traders asked gemological labs to describe the gems on lab documents as "paraíba" tourmaline. This forced labs to come up with a definition for this variety.
One proposal was to determine the coloring agent(s) for these unusual varieties. Quickly it was determined that copper played a major role, along with manganese. But building a variety definition based on composition alone is fraught with danger.
First, our knowledge of what creates color is fluid, constantly changing as new discoveries are made. Once upon a time, chromium was considered the only cause of color in emerald. We now know that vanadium also plays a role, sometimes the dominant one. Similarly, until quite recently, iron was thought to be a major cause of color in yellow sapphire; today we understand that color centers are more important.
Second, the color of finished gems is dramatically affected by all manner of things unrelated to composition, such as variations in size, cutting, inclusions and color zoning. Thus composition alone is problematic.
The LMHC has attempted to address these issues by building a definition that is both independent of origin and that incorporates color and composition (see LMHC Information Sheet #6). While the LMHC definition does not currently encompass stones in the violet-to-purple range, this could be a topic for future discussion. Currently, the AGTA GTC follows the LMHC definition.
Untreated purplish violet paraíba-type tourmaline from Mozambique. If heated, stones such as this often change to a rich blue-green color. |
Untreated electric green paraíba-type tourmaline from Mozambique. |
Does every tourmaline that contains a certain amount of copper/manganese qualify as a paraíba? In a word, no. The most important feature of a paraíba tourmaline is exactly that which made the gem famous in the first place – intensity of color. Thus if a gem submitted for testing lacks the necessary degree of color saturation, it will not meet the AGTA GTC's paraíba criteria, no matter what its chemistry. In such a case, color trumps chemistry.
A suite of tourmalines showing just a portion of the incredible color range of this gem. The blue-to-green gems in the center of the photo lack the necessary color saturation to qualify as paraíba. Photo: Wimon Manorotkul/Palagems.com |
Another issue is that of origin. While paraíba tourmalines were first found in Brazil's Paraíba State, stones of similar color and composition have now been found in Rio Grande do Norte State (Brazil), Nigeria and Mozambique. Some purists have argued that the paraíba variety should be limited to Brazilian stones, but the decision of the LMHC was that this variety will be defined by color and composition, not country-of-origin. Upon request, member labs of the LMHC will identify the country-of-origin on their documents, thus satisfying all clients.
Heat-treated neon-green paraíba tourmaline from Mozambique. Photo: Wimon Manorotkul/Palagems.com |
By Loretta Castoro, Richard Hughes and Hpone-Phyo K. Nyunt
The Fourier-Transform Infrared Spectrophotometer (FTIR) is used to help determine whether a sapphire has been thermally enhanced. The heights of the various peaks give the gemologist an indication of whether the sapphire being tested has been thermally enhanced. For example, when a strong peak at 3160 wavenumbers is found, this is an excellent indication that the sapphire being tested has not been thermally enhanced.
When a strong peak is found at 3309 in non-basaltic sapphire, this gives an indication that the gem may have been thermally enhanced. Interestingly, a weak-to-medium 3309 peak can be found in both heated and unheated sapphire. Thus great care must be given to analyzing FTIR data.
Two different FTIR methods are commonly used for testing gems. One involves a transmission scan, where a relatively narrow infrared beam is passed through the specimen. As a result of the restricted path, only a portion of the gem is sampled. Another technique, the Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) method, diffuses the beam throughout the gem and thus samples a greater portion of the piece.
We recently tested a 5.72-ct blue sapphire with both techniques. As one can see from the pictured spectra, the narrow-beam method produced a small peak at 3309. However when the DRIFTS method was utilized, a much stronger 3309 peak was found, suggesting that the gem was probably heat treated. This was later confirmed by examination of the inclusions.
FTIR spectrum of a 5.72-ct heat-treated blue sapphire taken with the beam condenser transmission method. |
FTIR spectrum of the same 5.72-ct heat-treated blue sapphire taken with the DRIFTS method. In this instance, the DRIFTS method was better able to unveil the strong 3309 peak. |
Why the two different results? By their very nature crystals possess directional properties and this can impact spectra of all sorts, including infrared. But more important, crystals are composed of layers of atoms stacked one on top of another. As the growth takes place, the conditions constantly change, from start to finish. Thus one layer is never identical to another. We can see this in the arrangement of inclusions within a crystal and it is most obvious in the growth and color zoning that many crystals display.
Differences in composition and structure from one layer to another create growth zoning and are also probably responsible for the different FTIR spectra we obtained in this specimen. In this particular gem, the DRIFTS method was better able to capture the full amplitude of the 3309 peak because it sampled a greater portion of the specimen.
Magna-ir 560 Nicolet FTIR |
The Smithsonian Visits the AGTA GTC Mobile Laboratory in Tucson
One of the great pleasures of AGTA GemFair™ Tucson is the chance to view so many fine gemstones under one roof. And if this were not enough, our staff also has the once-in-a-lifetime opportunity to physically examine actual museum specimens.
For several years, Russell Feather and Dr. Jeffrey Post of the Smithsonian Institution have organized private viewings for the AGTA GTC staff of the museum specimens on display at AGTA GemFair™ Tucson. This year we were not disappointed, as Russell Feather brought in several outstanding examples of why the Smithsonian Institution's National Gem Collection is one of the biggest draws in the world. Oo's and ah's were heard as one amazing piece after another was brought out for viewing and examination.
We extend our most sincere thanks to Russell Feather and Dr. Jeffrey Post for making these viewings possible, but have one teeny, tiny request: next year, Hope Diamond. Pretty puleeesse?
The Smithsonian Institution's Russell Feather shows off a stunning engraved emerald necklace during his visit to the AGTA GTC Mobile Laboratory during the 2007 AGTA GemFair™ Tucson. Photo: R.W. Hughes/AGTA GTC. |
Bulk Testing
Many of our clients may not be aware that we do offer bulk testing. Indeed, in just the past week we have completed bulk testing of a parcel of Sandawana emerald.
Fees for bulk testing are dependent on the material to be tested, the quantity of pieces and the specific information the client wishes to know. Contact us for more details.
Amphibole needles are a common occurrence in Sandawana emeralds, as the above photomicrograph shows. Photo: R.W. Hughes/AGTA GTC. |
Upcoming Lectures
AGTA GTC staff will be busy in the coming months, with the following lectures:
Pasadena, CA, Saturday, March 31, 2007 
- Jade: Stone of Heaven
Richard W. Hughes, AGTA Gemological Testing Center
Saturday, March 31, 2007, 2:00 PM
Pacific Asia Museum
46 North Los Robles Avenue, Pasadena, California 91101
Tel: 626-449-2742
Known to the Chinese as the "Stone of Heaven," jade is one of mankind's most beguiling gemstones. While the term "jade" includes both nephrite and jadeite, only jadeite occurs in the coveted "imperial" type, and for this the world has but one source, Upper Burma. It is these mines which are the subject of this program.
Burma's center of jade mining is the small town of Hpakan. Fortune-seekers from all over Asia are drawn to the mines and the heady atmosphere is one of the gold rush days of the old American West. Famous in Burma as "Little Hong Kong," Hpakan offers Hennessy cognac, Rolex watches, French perfume and much more. This is all the more amazing considering the difficulty of getting there, as it is located amidst some of the most impenetrable jungles on the planet.
In 1996, Richard Hughes was a member of the first foreign gemological party allowed into these mines in over 30 years and will regale participants with a first-hand account of the mining and trading of this fascinating gemstone.
Washington, DC, Monday, April 9, 2007, GIA Alumni, DC Chapter
- People & Places: New Directions in Gemology
Richard W. Hughes, AGTA Gemological Testing Center
Monday, April 9, 2007, 7:00 PM
Holiday Inn Rosslyn, 1900 Ft. Meyers Drive, Arlington, VA 22209
Tel: 202-342-3943
Gemology is tired. Weary. Stumbling. Guilty. We are privileged to work with some of the most stunning and romantic objects on the planet – singular marvels of incredible beauty. And yet all we can do is analyze. Like sadists, we torture beauty until the extraordinary is reduced to the ordinary – chemicals, numbers and digits – abstractions with no relation to the reasons why people are drawn to precious stones. We break the butterfly upon the wheel.
Which instrument comprehends feeling? What tool measures emotion? No device can see with our eyes nor read our minds. Yet we surrender our senses to the machine. Guilty as charged. We break the butterfly upon the wheel.
Gemology cannot be simply science. People are drawn to precious stones because of passions, not just properties. The purchase of a gemstone is an emotional contract that connects the new owner with people and places across the planet. If we wish to fathom desire, we must begin understanding this visceral link. And if answers are not easily measured, if they involve emotion and art, not just science, they are no less real and no less important to gemology.
Richard Hughes will delve into these issues via a dramatic multimedia presentation that covers ground all the way from Manhattan, through Russia's emerald mines, to Madagascar and Tajikistan's remote ruby, sapphire and spinel deposits.
It will provide inspiration, a new direction into the neglected, nether regions of gemology. Don't miss it.
Denver, CO, April 25–28, 2007, AGS Conclave 
- Solid Steps to Successful Colored Gemstone Sales
Douglas Hucker, AGTA
Friday, April 27, 2007, 11:00–11:45 AM
AGTA's Chief Executive Officer explores the critical components of a dynamic and successful colored gemstone jewelry presentation. What motivates your customer to buy color? What are their major concerns when doing so? Learn the basic components that must be included in every presentation to dramatically improve your success rate. Identify your most powerful sales tools, including a thorough discussion of the AGTA GTC Colored Gemstone Reports and the critical part they play in the sales presentation.
- AGTA Laboratory Highlights
Dr. Lore Kiefert, AGTA GTC
Friday, April 27, 2007, 3:45–4:45 PM
Join Lore Kiefert as she brings you up-to-date on current issues in day-to-day gemstone testing: the treatment of emerald, ruby, sapphire and pearls; new sources of these gemstones and the confusion when these first arrive on the market unnoticed; and the detection of synthetics and imitations. These challenges are presented using current examples the laboratory has encountered. Unusual and rare cases of gemstone testing also will be introduced.
- Take the Vow with Color
Douglas Hucker, AGTA
Saturday, April 28, 2007, 2:30–3:30 PM
Colored gemstones and cultured pearls have a rich tradition as betrothal gifts, and their presence in this all-important lifetime event is on the rise. This seminar will look back on the rich history of gemstones and cultured pearls in the wedding ceremony. Let's consider how you, the 21st Century American Gem Society jeweler, can introduce these beautiful treasures to your clients who are preparing to take the vow and "something old" indeed becomes "something new."
The AGTA Gemological Testing Center provides the industry and the public with a complete range of lab services including gemstone identification, origin determination and pearl identification. Located in New York City, the laboratory is equipped with the latest, technologically advanced, investigative equipment. The AGTA GTC is committed to providing excellent service, superior value and outstanding quality. A complete list of services and detailed pricing information is available on our website, www.agta-gtc.org. Please contact us with any questions.
