Feature

Gems & Gemology’s 7 Most Unusual Encounters from 2019


A face-up view of a cushion-cut diamond with blue colour.
Face-up image of the natural diamond with CVD synthetic diamond overgrowth. The blue colour is due to the boron-doped CVD layer. Photo by Robison McMurtry

Each year, GIA’s laboratories receive an enormous variety of diamonds and coloured stones for grading and identification and origin reports. Specimens that are rare or eye-catching or reveal unusual characteristics appear in the quarterly Lab Notes column of Gems & Gemology. Here are G&G’s seven most interesting and unusual from 2019.

1. Diamond on Diamond: CVD Layer Grown on Natural Diamond

A 0.64 ct Fancy greyish greenish blue cushion-modified brilliant showed two distinct fluorescence patterns, as well as characteristics of both type Ia and type IIb diamond. The specimen was found to be a composite of a CVD synthetic diamond layer on top of a natural diamond. This was only the second such composite seen at GIA, but it could represent a new type of product entering the market.

Dislocation bundles visible in CVD layer
Dislocation bundles in the CVD layer are visible under crossed polarisers in methylene iodide. Photo by Troy Ardon; field of view 1.90 mm.

2. Big Sky, Big Ruby: Large Montana Ruby

Montana’s secondary deposits produce sapphire in a wide range of mostly pastel colours. Pink sapphires from Montana are rare, and corundum with enough depth of colour to be called ruby are rarer still. A 1.70 ct purplish red octagonal modified brilliant was examined. Its colour and large size made it an exceptional specimen—only the second report for a Montana ruby issued by the lab to date.

Side-by-side images of inclusions in a Montana ruby.
Inclusions in the 1.70 ct ruby from Montana. Left: Close-up of a glassy melt inclusion with an associated thin film showing geometric patterns; field of view 1.76 mm. Right: A melt inclusion with an iridescent thin film, partial hexagonal zone of particles and short needles; field of view 3.81 mm. Photomicrographs by Claire Malaquias

3. V for Vanadium: High-Vanadium Colour-Change Burmese Sapphire

A 5.68 ct transparent cushion-mixed-cut sapphire displayed a strong colour change from greyish violet in fluorescent light to purple-pink in incandescent light. Chemical analysis showed an unusually high level of vanadium, the first time the Carlsbad lab had encountered a colour-change sapphire with this chemistry profile.

Side-by-side images of a cushion-cut sapphire. The left shows a greyish violet colour and the right a purple-pink colour.
This 5.68 ct cushion-mixed-cut sapphire showed a strong colour change from greyish violet in fluorescent light to purple-pink in incandescent light. Photo by Robison McMurtry.

4. Neon Faux: Paraíba-Like Synthetic Sapphire

Two gemstones, 7.78 and 4.90 ct, had a neon green-blue to blue-green colour similar to that of Paraíba tourmaline. Curved colour banding and Plato lines identified them as flame-fusion synthetic sapphire. This was the first time GIA’s Carlsbad lab had examined flame-fusion synthetic sapphire with a Paraíba-like colour.

Two cut and polished synthetic sapphires.
This 7.78 ct round brilliant and 4.90 ct cushion-cut brilliant displayed a blue-green and green-blue colour, respectively, that are reminiscent of Paraíba tourmaline. Photograph by Nathan Renfro

5. Not Easy Going Green: Rough Diamond with Fake Green Coating

Natural green diamonds are extremely rare. Their colour is typically caused by exposure to radioactive minerals and fluids, which is accompanied by green or brown patches called “radiation stains”. A 6.49 ct green crystal was found to have been coated with chromium oxide powder, followed by annealing of the powder to produce surface plates resembling radiation stains. While the coating was easily detected with magnification, this was a significant attempt to mimic the features of natural green diamonds.

A green rough crystal.
This 6.49 ct rough diamond with patchy green surface colour was submitted to GIA’s Carlsbad laboratory for a Coloured Diamond Grading Report. Photo by Diego Sanchez

6. Stellar Stellate: Diamond with Remarkable Stellate Cloud

A 3.70 ct faceted Fancy brownish greenish yellow diamond contained an eye-visible stellate cloud inclusion consisting of six legs that each radiated to a point on the polished octahedron. This “asteriated” diamond was striking due to the well-defined nature of the star and the strong yellowish green colour it exhibited under long-wave UV. The faceted octahedron cutting style was unconventional, but served to showcase the inclusion scene contained within the diamond.

Side-by-side images of a Fancy brownish greenish yellow diamond. Left is normal light and right is under long-wave UV light.
This 3.70 ct brownish greenish yellow faceted octahedron contained a remarkable stellate hydrogen cloud (left) that showed strong yellowish green fluorescence under long-wave UV light (right). Photos by Diego Sanchez

7. Mega Stars: Large Laboratory-Grown Star Ruby and Sapphire

Two unusually large loose stones with asterism—a 4,759 ct red sphere with a diameter of approximately 76.96 mm, and a 467.2 ct blue cabochon measuring approximately 52.04 × 42.29 × 20.89—were identified as synthetic ruby and synthetic sapphire. While synthetic star corundum is not particularly rare, these were among the largest laboratory-grown star rubies and star sapphires submitted to GIA.

A large synthetic star ruby, left, and smaller synthetic star sapphire.
A 4,759 ct synthetic star ruby and a 467.2 ct synthetic star sapphire were submitted to GIA’s Tokyo lab. Photo by Shunsuke Nagai

Make sure you take a look at every issue of Gems & Gemology for more interesting and unusual Lab Notes.

Stuart Overlin is the managing editor of Gems & Gemology. Brooke Goedert is a writer/editor for gemmology content strategy at GIA. Kellie Giordano is the digital communications manager at GIA.