Lab Notes
Gems & Gemology, Fall 2017, Vol. 53, No. 3

Flux-Grown Pink Synthetic Sapphire with Unusual
Crystal Inclusions

Claire Ito
Flux-grown pink synthetic sapphire with unusual inclusions.
Figure 1. This pink stone proved to be a flux-grown synthetic sapphire with unusual crystal inclusions. Photo by Robison McMurtry.

The Carlsbad laboratory recently received a saturated pink cushion mixed cut, mounted in a ring, that measured 14.02 × 10.35 × 6.24 mm (figure 1). Standard gemological testing yielded a refractive index of 1.760–1.768 and a weak ruby spectrum using a handheld spectroscope, properties consistent with pink sapphire. The stone displayed a strong orange fluorescence under long-wave UV and an odd chalky orangy yellow fluorescence under short-wave UV. While orange fluorescence is not unusual in pink sapphires, the intensity and the chalky yellow reaction were suspicious. 

Microscopic examination revealed a single hexagonal, dark reflective platelet (figure 2); numerous transparent, colorless tabular to rounded doubly refractive crystals (figure 3) that showed interference colors under crossed polarizers; and a small fingerprint composed of elongated tubules. Observation in immersion showed some weak, straight orange and pink zoning. This inclusion scene could easily be mistaken for natural as the transparent crystals bore a certain resemblance to zircon, a common inclusion in natural sapphires and particularly pink sapphires from Madagascar. The dark reflective platelet, which was presumably platinum, and odd fluorescence prompted further investigation.

Platinum platelet is a common inclusion in flux-grown synthetic corundum.
Figure 2. This dark reflective platinum platelet observed in the pink synthetic sapphire is a common inclusion in flux-grown synthetic corundum. Photo by Nathan Renfro; field of view 1.82 mm.
Transparent crystals and crystal clusters in synthetic sapphire.
Figure 3. The abundance of transparent crystals and crystal clusters could easily be mistaken for a natural inclusion scene in a pink sapphire from Madagascar. Photo by Nathan Renfro; field of view 1.79 mm.

The synthetic nature of the sapphire was confirmed using laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS). High amounts of Pt were detected, which would support a flux synthetic growth process. Small amounts of Fe and Be were present; Ga, Ti, and V were not detected. This chemical profile also supports synthetic sapphire. 

Transparent crystals of possible chrysoberyl (BeAl2O4) have been previously cited in flux-grown synthetic corundum (R.E. Kane, “The gemological properties of Chatham flux-grown synthetic orange sapphire and synthetic blue sapphire,” Fall 1982 G&G, pp. 140–153). In that case, Chatham stated that heavy concentrations of beryllium were added to the original aluminum oxide formula, which would explain the presence of those crystals. In our pink sapphire, none of the crystals reached the surface, so we were unable to identify them with Raman spectroscopy. Small amounts of beryllium were detected, so chrysoberyl could be a possibility in this case as well.

The presence of these natural-looking crystals combined with the general lack of other inclusions for a stone of this size, particularly diagnostic flux fingerprints, could make correct identification very difficult for gemologists without access to advanced instrumentation. This is one case where advanced testing in a well-equipped gemological laboratory was necessary to make a conclusive identification.

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