GIA Labs reports receiving 2 Moissanites submitted as diamonds

New York—Two stones submitted as natural diamonds to two different GIA labs turned out to be moissanite, the institute reported in the latest issue of its research journal.

According a lab note written by Courtney Robb and Sarah Arden in Gems & Gemology Fall 2022, a client recently submitted a 7.42 carat blue-green crystal to the New York lab for a Colored Diamond Identification and Origin Report.

The lab identified the stone as a synthetic moissanite crystal that had been sculpted to resemble natural rough diamond.

Synthetic moissanite can be easily confused with natural diamonds, the authors wrote, both because it may physically resemble them and has a similar density and weight.

(Although natural moissanite does exist, the crystals are small and fragmented, Robb and Arden noted in the paper; no gem-quality specimens have been found.)

In the case of the specimen sent to its New York lab, the GIA identified synthetic moissanite using Fourier Transform Infrared (FTIR) spectroscopy, with the resulting data showing a distinct moissanite spectrum, it said. he declares.

They confirmed the finding with a Raman spectrum analysis.

Interestingly, the synthetic moissanite was shaped into what the GIA called a “gently rounded octahedron with prominent stepped edges.”

Octahedra belong to the cubic crystal system, but natural and synthetic silicon carbides – which include moissanite – belong to the trigonal system and always display prismatic to tabular hexagonal crystal forms.

Natural diamond octahedra that have been partially resorbed by kimberlite magma can have various shapes and textures, as seen in this natural green diamond, known as “Matryoshka”, with resorbed tips and edges, and a trigonal engraving on its faces. Photo credit: Jian Xin (Jae) Liao

For this reason, the GIA concluded that the synthetic moissanite rough had been carved into an octahedron and the details – stepped edges and coarse texture – had been chosen to mimic the appearance of a natural diamond octahedron that had been partially resorbed by kimberlite magma, as seen above. .

The example is a reminder, the GIA said in its paper, that care should be taken when identifying gemstones, as such processes could be used to mislead customers and “damage the integrity of gemstone trading.” precious stones”.

A separate article on lab notes by Shoko Odake in the same issue of Gems & Gemology detailed how the GIA lab in Mumbai, India recently received a 1.71 carat square modified brilliant cut stone for a matching service.

His belt bore the inscription “GIA” and a number that matched an existing report number for a 1.71-carat natural square modified brilliant-cut diamond, but the font was different from that used for the actual GIA inscriptions.

After a gemological and spectroscopic examination, the GIA was able to confirm that the stone was in fact a synthetic moissanite.

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Sarah C. Figueiredo