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| The rounded edges on this large inclusion in the table of a 0.99 ct yellow round brilliant are indicative of synthetic origin. |
From the time they were first produced, synthetic diamonds have been a source of concern for the gem and jewelry industry. With the release into the market of gem-quality synthetic diamonds by Gemesis Corp. and other manufacturers, these concerns have grown considerably. In the Winter 2002 issue of Gems & Gemology (pp. 301–309), J. E. Shigley et al. described Gemesis yellow synthetic diamonds and the clues for their detection. Although identification may require advanced spectroscopic or luminescence equipment that is only available in a well-equipped gemological laboratory, in many cases the trained gemologist can make the separation based on standard gemological clues, such as metallic inclusions and color zoning. Such was the case with two yellow brilliants that were submitted to the East Coast laboratory for grading.
On examination with a microscope, both were immediately suspected of being synthetic. The first, a 0.99 ct round brilliant, had a very unusual inclusion under the center of the table (see figure). When viewed from various angles, this pyramid-shaped inclusion was seen to be very dark gray to black with rounded edges—in contrast to the pyramidal or octahedral inclusions that may be seen in natural diamonds, which typically are transparent or white with flat surfaces and sharp edges. On the basis of its appearance, we concluded that this somewhat globular inclusion was a remnant of metallic flux, which is not uncommon in synthetic diamonds grown by a high pressure/high temperature process. During this growth process, the carbon source is dissolved in a molten metal, or flux, typically composed of iron, nickel, and cobalt. This flux facilitates the movement of carbon atoms toward a host seed crystal, where they are deposited to form a larger crystal. Sometimes pieces of the molten material are trapped inside the growing synthetic diamond as inclusions, taking on diamond’s octahedral crystal form while still exhibiting the melted appearance and rounded edges that are characteristic of a metallic flux.
The second sample, a 1.41 ct square modified brilliant, also had a black inclusion. In this instance, the inclusion reached the crown surface, and had been partially polished away. The remnant visible at the surface did not look so unusual, but the internal portion was globular in appearance, with rounded, elongated protrusions penetrating a short distance into the diamond. Again, such rounded black opaque inclusions are indicative of synthetic origin. As a further test, a strong magnet was used to verify that the inclusion was indeed metallic, as all three of the elements typically used in the flux are usually magnetic. Further observation of this synthetic diamond revealed color zoning and a cloud of minute pinpoint inclusions. Both of these characteristics are typical of synthetic diamonds. We confirmed the synthetic origin of these two samples with the De Beers DiamondView luminescence imaging system.
Vincent Cracco and Joshua Sheby
GIA Gem Laboratory, New York
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