AGTA GTC Laboratory Update
Nov 18, 2008
In this message…
- Unusual Ring from Christie’s
- Rubies from Winza, Tanzania
- Update on Red Andesine/Labradorite
- AGTA GTC offers new Emerald Seminar
- Prepare for the Holiday Season
Unusual Ring from Christie’s
Recently, we were asked to identify the gemstones used in an unusual ring. The ring was in the shape of a snail (Photo 1), consisting of small pink and purple gemstones, and signed “A. Soldier”. Almost all of the purple gemstones were clean, but some of the pink faceted gemstones showed typical tourmaline fingerprints. A random Raman analysis on the pink gemstones confirmed tourmaline; the purple ones were identified as amethyst. The larger cabochon in the middle of the snail shell was identified as pyrope-almandine garnet. In the microscope, the cabochon produced an interesting effect, by mirroring the surrounding gemstones, so that it looked like an insect eye (Photo 2). This ring is to be auctioned by Christie’s New York in February 2009.
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Fig. 1: This ring was submitted to the AGTA GTC to identify the pink and purple gemstones. Photo: Lore Kiefert, ©AGTA GTC |
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Fig. 2: In the microscope, the cabochon acts as a mirror to reflect the other gemstones. Photo: Lore Kiefert, ©AGTA GTC |
With the Tom Lantos Block Burmese JADE Act in effect since September, gemstone dealers are looking for alternative sources to supply their clients with rubies. One such source is Winza in Tanzania. This area has only been producing fine gemstones for several months. Some of these rubies are very clean, and with the limited exposure to these goods, it can be difficult for a laboratory to come up with a positive identification of origin.
That being said, a 5.07 carat oval ruby with an unusual surface feature was submitted to AGTA GTC for a country of origin report. The ruby was unique in its size and it was free of inclusions except for one growth tube touching the crown surface. Typical growth zoning features found in natural ruby were not immediately apparent. EDXRF confirmed that the ruby was natural and was of East African origin, possibly from Tanzania. The pavilion of the stone had an asymmetrical outline with a flattened area that exhibited a surface which appeared melted. Our initial impression was that the ruby was subjected to thermal enhancement (Fig. 1).
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Fig. 1: Melted surface on an otherwise clean ruby. Photo: Susan Paralusz, ©AGTA GTC |
The client subsequently conveyed to us that the ruby was unheated and from the Winza mines in Tanzania. Two other rubies from the same source, a 6.09 ct pear shape and a 2.25 ct oval, were supplied by the client for research purposes. We confirmed with colleagues that rubies from the Winza mines may exhibit a surface that appears melted in natural unheated rough, which is usually removed in the manufacturing process. The 6.09 carat pear shape ruby also exhibited this melt feature along with some fractures and a needle touching a star facet (Fig. 2).
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Fig. 2: Only a few fractures in a 6.09 ct pear-shaped ruby (top) demonstrate the high quality of this new Winza material. Photo: Susan Paralusz, ©AGTA GTC |
The 2.25 ct oval ruby featured a fingerprint, several fractures and straight growth features sometimes found in rubies from Tanzania (Fig. 3).
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Fig. 3: These types of fingerprints are typical for rubies from Winza. Photo: Susan Paralusz, ©AGTA GTC |
Reportedly, rubies from Winza also exhibit a moderate peak at approximately 3158 cm-1 in the FTIR, which all three of the sample rubies displayed. This feature is well known from unheated yellow or padparadscha sapphires, but has never been observed in any ruby from another source.
Based on the information we collected we issued a report for the 5.07 carat oval ruby stating that the ruby was natural with no indications of thermal enhancement and Tanzania as the country of origin.
Update on red andesine/labradorite
During the last Laboratory Manual Harmonization Committee (LMHC) meeting in Tokyo in September, the laboratories exchanged information about their research on andesine/labradorite. Most laboratories are doing some research on these samples, but at GIA and GAAJ-Zenhokyo the subject has become a major research project.
While it was clear by then that copper can be diffused into andesine/labradorite, the question remained if there was any source of natural red andesine/labradorite. GAAJ-Zenhokyo's Ahmadjan Abduriyim showed andesine/labradorite from two different origins; yellow samples from Inner Mongolia and red samples from Tibet. Ahmadjan recently visited both mines. He confirmed that there is no red material coming out of the Mongolian mine (Figs. 1, 2).
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Fig. 1: Mining area in Inner Mongolia. Photo: Ahmadjan Abduriyim, ©GAAJ-Zenhokyo |
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Fig. 2: Yellow andesine/labradorite from Inner Mongolia. Photo: Ahmadjan Abduriyim, ©GAAJ-Zenhokyo |
The GAAJ-Zenhokyo Lab also talked to gemstone dealers, who admitted to diffusing the material from Inner Mongolia. Zenhokyo Lab also obtained some Cu-diffused red andesine/labradorites from Japan-Germany Gemmological Laboratory (JGGL) which had been treated in Thailand (Fig. 3). Some of the samples showed only shallow diffusion, while others were diffused further into the gemstone. During his trip to China, Ahmadjan confirmed that the majority of the yellow samples are treated in China using Co-60 radiation or Cu-diffusion.
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Fig. 3: Diffused andesine/labradorite from Inner Mongolia. Photo: Lore Kiefert, ©AGTA GTC |
The second set of samples that were shown was red andesine/
labradorite in a bag with the soil from Tibet (Fig. 4).
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Fig. 4: Soil nodule and bags containing natural colored andesine/labradorite from Tibet. Photo: Ahmadjan Abduriyim, ©GAAJ-Zenhokyo |
The Tibetan soil contained nodules, which we broke apart and retrieved red water-worn crystals. At that time, we were still doubtful if these gems had been placed into the soil beforehand, or if they were indeed in situ. This question was answered by Ahmadjan, who had the chance to visit the mine in Tibet. He confirmed that red andesine is indeed found in situ in the soil nodules as presented (Figs. 5, 6). The original deposit is volcanic, but erosion caused the crystals to be transported and deposited in a yellowish soil.
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Fig. 5: The andesine/labradorite mine in Tibet. Photo: Ahmadjan Abduriyim, ©GAAJ-Zenhokyo |
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Fig. 6: A close-up of the andesine/labradorite bearing soil from Tibet. Photo: Ahmadjan Abduriyim, ©GAAJ-Zenhokyo |
Since the red andesine found in Tibet is largely identical to the treated Mongolian material, the laboratories are now challenged to find a way to separate the two from each other. Until we are able to clearly distinguish the diffused from the natural red andesine/labradorite, we will not be issuing reports on this material.
With the great success of our Corundum Treatment Seminar, the AGTA GTC has developed an Emerald Treatment Seminar. This seminar combines emerald treatments and emerald origins, but the focus is on treatments. The seminar provides an overview on historic and modern emerald treatments. The seminar participant will learn how to visually identify the nature of the filler, as well as the extent, through hands-on examination of actual emerald samples. The GTC staff will demonstrate the advanced instruments it takes to perform safe filler identification.
The second part of the seminar demonstrates how microscopic evidence can determine the origin of the emerald, again with hands-on demonstrations. Knowing the origin can help narrow down the type of filler used, as every country has its own preferred filler material.
The first Emerald Treatment Seminar will take place in New York at the AGTA GTC office on December 3rd. Maximum attendees: 6, Price $800.
Further classes will be scheduled in conjunction with the Corundum Treatment Seminar. For participants wanting to attend both days, a reduced rate of $1250 applies. For the exact dates of next year’s classes, please visit our website www.agta-gtc.org. Further seminars on corundum origin determination and pearls are being developed.
The holiday season is approaching fast. In order to help you with your sales, the AGTA GTC is offering a 10% discount for the submission of 10 or
more gemstones. A great sales tool for high-end gemstones is the JewelFolio™, a customized 32 – 48 page cloth or leather-bound report that accompanies your gemstone.
JewelFolio™ is currently offered on Burma rubies, Burma sapphires, Kashmir sapphires, Sri Lanka sapphires, Colombian emeralds, and Tanzanite. The text provides history, lore, photos of the mines, inclusion photos, followed by the individual data of your gemstone, AGTA GTC origin report, including an inclusion photo and spectra results. The turnaround time for the Jewelfolio™ is currently four weeks, so get your gemstones in now.
For more information on the JewelFolio™ and other services, please visit our website www.agta-gtc.org, or call us at 212-752-1717.
