AGTA GTC Laboratory Update
Nov 18, 2008
In this message…
- Unusual ring auctioned by Christie’s New York next February
- Rubies from Winza, Tanzania
- Update on Red Andesine/Labradorite
- AGTA GTC offers new Emerald Seminar
- Prepare for the Holiday Season
Unusual ring auctioned by Christie’s New Yor next February
Recently, we were asked to identify the gemstones used in an unusual ring. The ring had the shape of a snail (Photo 1), consisting of small pink and purple gemstones, 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 could be identified as amethyst. The larger cabochon in the middle of the snail house 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).
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Fig. 1: This ring in the shape of a snail 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 Burma ban in place since September, gemstone dealers are looking for alternative sources in order to supply their clients with rubies. One such source is Winza in Tanzania, a ruby source which has been producing fine gemstones only since this year. Some of these rubies are very clean, and not having seen many of these, it can sometimes be hard for a laboratory to come up with the right answer.
A 5.07 carat oval ruby from this source with an unusual surface feature was submitted to AGTA GTC for a country of origin report. The ruby was unique in its size and that 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 then conveyed to us that the ruby was unheated from the Winza mines in Tanzania and subsequently dropped off two other rubies, a 6.09 ct pear shape and a 2.25 ct oval, for research purposes from the same source. 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 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 our 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 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 is any source of natural red andesine/labradorite.
GAAJ-Zenhokyo's Ahmadjan Abduriyim showed us samples of andesine/labradorite from two different origins, one being yellow samples from Inner Mongolia. Ahmadjan recently visited the mine and confirmed that there is no red material coming out of there. When talking to the locals, they were not sure what happens to their material once it leaves Inner Mongolia, but mentioned three different types of treatment: heat, irradiation, diffusion.
The GAA-Zenhokyo Lab also talked to gemstone dealers, who
Figure 1 |
admitted to
have diffused the material from Inner Mongolia. Zenhokyo Lab also collected some Cu-diffused red andesines from Japan-GermanyGemmological Laboratory (JGGL) which have been treated in Thailand(Fig. 1). Some of the samples showed only shallow diffusion, while others were diffused
Figure 2 |
further into the gemstone.
Chemical analysis of a slide that Ahmadjan presented showed that the copper content at the rim of the samples was high and low in the center throughout a cross section (Fig. 2).
The second set of samples was red andesine in a bag with the soil from Tibet (Fig. 3). The Tibetan soil contained nodules,
Figure 3 |
which we broke apart and retrieved red water-worn (or tumbled) crystals (Fig. 4). At that time, we were still doubtful if these gems have been placed into the soil beforehand, or if they were indeed in situ. Meanwhile, this question was answered by Ahmadjan, who had the chance to visit the mine in Tibet
Figure 4 |
together with a colleague and some people from JTV, who sponsored the expedition. We have now confirmation that red andesine is indeed found in situ in Tibet. The original deposit is volcanic, but erosion caused the crystals to be transported and deposited in a yellowish soil.
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.
AGTA GTC offers new Emerald Seminar
The first Emerald Seminar will take place in New York at the AGTA GTC Premises on December 3rd. Maximum attendees: 6, Price $800.
From January on, further classes are 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 on pearls are planned.
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 also the JewelFolio, a book to go with your gemstone.JewelFolios are only issued for Burma rubies, Burma sapphires, Kashmir sapphires, Sri Lanka sapphires, Colombian emerald, and Tanzanite. They consist of over 30 pages, with a historical overview, photos of the mines, inclusion photos in the first half of the book, followed by individual data of your gemstone, including an inclusion photo and spectra. For more information on the JewelFolios and other services, please visit our website www.agta-gtc.org, or call us at 212-752-1717.
