corundum, quality.9, gems

News from the Bangkok gem market.

corundum, Burma.12, gems

As many of our readers are well aware, the area around Mogok in Upper Burma is the world's premier source for rubies. Since 1962, however, it has been closed off to the outside world, merely adding to the mystery of a place already steeped in legend. With the utmost difficulty we have succeeded in obtaining modern pictures of Mogok

corundum, treatments.6, gems

Describes an unusual ruby where glass was used to fuse one piece of natural ruby to a much larger piece of synthetic ruby. A second ruby appeared to have glass in fissures throughout. [in hindsight, this was probably exsolution of planes of boehmite or another mineral]

gems, corundum, color.4

The phenomenon of pleochroism in doubly refractive (DR) gemstones is described, as it relates to overall color appearance in the context of faceted gems. With strongly pleochroic gems, pleochroism can be seen in faceted gems, even if the table facet is oriented perpendicular to an optic axis. This is because facets change the direction of light as it moves through the gem.

corundum, star sapphire, quality.9, gems

During 1986, newspaper reports told of a most Incredible gem find. Mr. Roy Whetstine of Longview, Texas, went to the 1986 Tucson Gem and Mineral Show hoping to find a few pretty rocks for his two sons. He returned home with what he claimed to be the world's largest rough star. sapphire, bought for $10 from a bowl full of agates, and later appraised at $2.28 million. It was an amazing story and one that warmed the hearts of thousands of readers around the.world -a little man strikes-a bonanza! Slowly, however, clouds began to form and before long they were pouring down rain on Mr. Whetstlne's parade. What occurred was the exposure of one of the most ambitious gem cons of the twentieth century.

corundum, yellow sapphire, sapphire, treatments.6, synthetic gems.7, gems

This article describes two techniques for identifying yellow sapphire. The first uses a blue filter to detect color zoning in natural and synthetic yellow sapphire. Second is how gently heating heat-treated yellow sapphires under a lamp will cause their color to temporarily darken. It can thus be used to separate heated yellow sapphires from natural yellow sapphires.

corundum, treatments, jade, jadeite, fei cui, assembled stones.8, ruby imitations, ruby, gems

A plastic coated jadeite cabochon and a quartz coated with red plastic to imitate ruby are described.

corundum, History.1, gems

The gemstones believed to have been known in Classical Antiquity – their mineralogical identities and their geographic sources – were inferred almost exclusively from literary sources until the turn of the 20th century. Typological and thematic classifications of ancient glyptic were first proposed in Adolph Furtwängler’s monumental work, Die antiken Gemmen (1900), and for the first time objective empirical criteria were employed to organise gemstones according to their materials. Furtwängler set a standard that gem scholars would follow and develop further. Gem catalogues came to feature a materials index, comparanda of materials related to engraved subjects, and typologies of gem and jewellery shape, toolwork, and carving style. Analysis of distribution patterns of gem materials revealed cultural preferences for specific gemstones and also artists’ and workshop associations, which improved the overall picture of the gemstones used in different periods of Classical Antiquity. Gems and jewellery recovered from archaeological contexts enabled firmer dating and cultural attribution of glyptic otherwise based on iconographic or stylistic features. This is a superb article. Highly recommended.

gems, corundum, treatments.6, Australia.12

The late Geoff Tombs was always interested in heat treatment, publishing several papers on the subject (Tombs 1978, 1979, 1991). However the paper that sticks in my mind the most was written in 1974 and titled ‘Synthetic-like fluorescence in a natural sapphire’ Tombs 1974. At the time of writing I suspect Geoff While describing a Fine blue Ceylon sapphire submitted for testing………., Geoff was surprised by the results he obtained when examining the stone under UV light, summing up his report: Microscopic examination proved the stone to be natural. This stone is particularly interesting as it is the first naturai sapphire I have examined in which blue sections showed fluorescence characteristics exactly the same as those exhibited by the typical Verneuil synthetic blue corundum. The fluorescing areas (under S/W) were curious in that they did not follow the blue colour zoning. (Tombs 1974). In hindsight I believe Geoff was examining a heat-treated Ceylon blue sapphire a few years before such a treatment became generally known amongst the gemmological community. Most importantly, he recognised that here was something different enough to be worth reporting in his favourite magazine, The Australian Gemmologist. I dedicate this paper to him. I would like you to join me in tracing the lives and interests of several people associated with Australian sapphire. They come from widely differing backgrounds and cultures. Some are university educated, while some never went to school. Some are even still alive today. It is through their fascinating testimonies that I have been able to put this story together.

gems, spinel, Vietnam, Luc Yen, Mogok, Burma, Myanmar

This study investigated the gemological characteristics of red and orange spinel from Mogok in Myanmar and from Lang Chap and An Phu in Vietnam. In terms of standard gemological properties, all samples displayed a refractive index ranging from 1.710 to 1.728, specific gravity of 3.528 to 3.692, and red fluorescence under ultraviolet light. Advanced gemological methods, including ultraviolet/visible/near-infrared spectroscopy, electron probe microanalysis, and laser ablation–inductively coupled plasma–mass spectrometry, were employed to investigate chemical compositions, particularly focusing on chromophores and determination of diagnostic origin criteria. Both red and orange spinel samples exhibited chemical properties close to stoichiometric spinel. It was found that the diverse coloration in red and orange samples resulted from variations in chromium-to-vanadium ratios. The studied red spinels were chromium-rich, with chromium-to-vanadium ratios ≥1.7, whereas the orange spinels were vanadium-rich, with chromium-to-vanadium ratios ≤1.0. Trace element plots of titanium versus zinc for red spinel revealed separation between the three sources (Mogok, Lang Chap, and An Phu). Regarding orange spinel, plotting of vanadium versus zinc showed separation for Lang Chap and An Phu samples but due to the wide range of composition found in the Mogok samples, there was overlap between samples from Mogok and the two Vietnamese sources. Therefore, separation of the orange spinel from these sources is more difficult and will require investigating additional samples.