Writing in the latest issue of Gems and Gemology, the journal of the Gemological Institute of America (GIA), Rebecca Tsang, a gemologist at the institute in Carlsbad, California, reports that the lab recently came across a synthetic moissanite sample that resembled a rough diamond.

Clarifying that there was no evidence that “this specimen was deliberately deceptive”, the report said that the nature of the gem was established only after “closer examination of its habit and surface features, along with gemological and advanced testing results”. GIA said that the “very light green 9.71 ct specimen, measuring 11.79 at × 9.69 × 11.61 mm, resembled a diamond octahedron, with surface growth features and a bright vitreous to subadamantine luster”.

In the report, Tsang writes that “the specimen was not a true octahedron, as is typical of a diamond crystal, but a rectangular bipyramid with 10 faces (eight triangular and two hexagonal side pinacoids on the girdle)”.

The dimpled surface, with two faces having deep striations resembling growth features in a rough diamond; irregularly shaped and sub-hexagonal etch pits, along with some dark brown residue on the surface; and the uneven surface initially limited the observation of internal features.

However, when it was viewed in plane-polarized light, proof emerged of the stone’s doubly refractive nature, as opposed to singly refractive diamond, while standard gemmological properties of the stone offered further evidence of its true identity.

Along with the results of advanced testing, including Fourier-transform infrared (FTIR) and Raman spectrometry, the stone was identified as synthetic moissanite.

The lab concludes that this reveals how indispensable gemological and advanced testing are “for revealing the true identity of gems, especially simulants and imitations with an appearance that can easily deceive the general public”.

Pic caption: A very light green 9.71 ct synthetic moissanite crystal, submitted to the Carlsbad laboratory as a rough diamond. Photo by Rebecca Tsang; field of view approximately 14 mm.

Courtesy: GIA