An Unusual Doublet Set in Fine Jewelry
The pavilion showed fingerprint-like inclusions consisting of droplets that were easily visible with the loupe (figure 3). This feature might lead one to believe it was a flux synthetic emerald, inconsistent with the observations on the crown. Magnification reveals, however, that the fingerprint-like inclusions are actually made up of very small cavities, with bubbles that are clearly visible in the larger cavities. Therefore, the pavilion is actually a natural gem.
At the level of the girdle, close examination revealed one area with a separation line, hidden elsewhere because of the closed setting (figure 4). Through the table, small but prominent black spots occurred on a single plane. These were flat bubbles in cement introduced at the separation plane.
Only the crown appeared a weak red under the Chelsea filter. Under short-wave ultraviolet radiation, the upper part was inert while the lower part showed a light blue, milky luminescence. Under long-wave UV, both were inert. Therefore, the green oval was clearly a doublet (R. Webster, Gems: Their Sources, Descriptions and Identification, 4th ed., rev. by B.W. Anderson, Butterworths, London, pp. 457–468). The refractive index was impossible to measure on either the table or the pavilion because the prongs extended into these two areas.
Raman spectroscopy with a 514 nm laser and 4 cm–1 resolution identified the crown as beryl and the pavilion as topaz. Hence the central stone of the ring is a doublet with a hydrothermal synthetic emerald top and a topaz bottom, which is quite unusual.
This case is consistent with an earlier report (J. Hyršl and U. Henn, “Synthetische smaragd-topas-dublette,” Zeitschrift der Deutschen Gemmologischen Gesellschaft, Vol. 60, No. 3–4, pp. 111–112), which noted that the doublets were of Indian origin. The luminescence of the topaz bottom is slightly different in the present doublet, though still within the known variations of topaz luminescence.
Today far fewer doublets are being submitted to gemological laboratories. This specimen’s unusual setting, closed at the girdle and with large prongs preventing access to the table and pavilion for refractometer measurement, suggests an intent to disguise the composite (and partially synthetic) nature of the central gem. Even fine jewelry can be set with gems that are not natural, and gemologists should remain wary of doublets.