Lab Notes Gems & Gemology, Winter 2015, Vol. 51, No. 4

Synthetic Rock Crystal Quartz Bangle with Unusual Inclusions

Synthetic quartz bangle examined in Bangkok.
Figure 1. A synthetic rock crystal quartz bangle measuring approximately 80 × 22 × 10 mm. Photo by Nuttapol Kitdee.

Synthetic quartz is grown by the hydrothermal technique, which can produce large single crystals of high quality (K. Byrappa and M. Yoshimura, Handbook of Hydrothermal Technology: A Technology for Crystal Growth and Material Processing, William Andrew Publishing, 2001). This process, widely used in the jewelry trade, has led to difficulty in separating synthetic quartz from its natural counterpart (R. Crowningshield et al., “A simple procedure to separate natural from synthetic amethyst on the basis of twinning,” Fall 1986 G&G, pp. 130–139). The presence of Brazil-law twinning and certain inclusions, such as tourmaline or golden rutile needles, can be used to distinguish natural from synthetic quartz. But high-quality quartz, whether of natural or synthetic origin, typically has no inclusions or twinning. In this case, standard gemological testing may not be able to identify the origin. Advanced instruments, including infrared absorption spectroscopy (S. Karampelas et al., “An update in the separation of natural from synthetic amethyst,” Bulletin of the Geological Society of Greece, 2007, pp. 805–814) and LA-ICP-MS are considered useful tools for separating natural from synthetic material from material with synthetic origins (C.M. Breeding, “Using LA-ICP-MS analysis for the separation of natural and synthetic amethyst and citrine,” GIA News from Research, 2009).

The Bangkok lab recently examined a high-clarity, transparent, near-colorless bangle (figure 1). Standard gemological testing revealed a spot RI of 1.54 and an SG of 2.65, consistent with quartz. Magnification revealed irregular two-phase inclusions (figure 2). These inclusions are more likely to be present in natural quartz than in hydrothermal synthetic quartz, which typically shows nail-head spicule and breadcrumb inclusions. This bangle also gave an IR absorption spectrum unlike that of natural rock crystal quartz. The charac­teristic IR absorptions of natural rock crystal quartz occurred at 3379, 3483, and 3595 cm–1. These features are never seen in synthetic rock crystal quartz. The IR spectrum of the bangle showed absorption peaks at 3610, 3585, 3431, 3294, and 3194 cm–1 (figure 3), which matches the IR absorption features of synthetic rock crystal quartz (P. Zecchini and M. Smaali, “Identification de l’origine naturelle ou artificielle des quartz,” Revue de Gemmologie, No. 138/139, 1999, pp. 74–80). The IR spectrum confirmed that this material was grown by hydrothermal methods.

Two-phase inclusions seen in synthetic quartz bangle.
Figure 2. Irregular two-phase inclusions seen in the bangle using darkfield illumination (left and right) are similar to those found in natural specimens but are rarely found in hydrothermal synthetic quartz. Photo by Nattida Ng-Pooresatien; field of view 4.1 mm.
IR spectra comparing natural and synthetic quartz.
Figure 3. Infrared spectra of the synthetic rock crystal quartz bangle and a 17.50 ct natural rock crystal quartz faceted bead show different absorption patterns. The characteristic absorptions of natural rock crystal quartz at 3379, 3483, and 3595 cm–1 are never seen in synthetic rock crystal quartz. The bangle showed absorption peaks at 3610, 3585, 3431, 3294, and 3194 cm–1, matching the IR absorption of synthetic rock crystal quartz.

Large transparent colorless quartz can be found in natural and synthetic forms, but synthetic quartz is usually seen as a flat crystal. This bangle is an interesting example of large, high-clarity synthetic quartz used in jewelry. The presence of the irregular two-phase inclusions in this example serves as an important reminder that natural and synthetic quartz can show a similar appearance and contain internal inclusion features that are identical.

Nattida Ng-Pooresatien is a staff gemologist at GIA in Bangkok.