Lab Notes Gems & Gemology, Spring 2015, Vol. 51, No. 1

Synthetic Moissanite Melee in a Colored Diamond Bracelet

Bracelet with moissanites
Figure 1. This fancy-color melee diamond bracelet contained two synthetic moissanites. Photo by Sood Oil (Judy) Chia.

A colored diamond bracelet submitted to the New York laboratory for identification (figure 1) contained 162 round brilliants ranging from 0.05 to 0.20 ct, with a color range from near-colorless to fancy yellow and brownish yellow. Melee-size diamonds below 0.20 ct are usually not screened for synthetics and imitations, and melee set into fine jewelry are very seldom tested due to limitations from the mounting. But because of recent concerns over fine diamond jewelry set with melee-size synthetics and imitations (see H. Kitawaki et al., “Identification of melee-size synthetic yellow diamonds in jewelry,” Fall 2008 G&G, pp. 202–213; Winter 2014 Lab Notes, pp. 293–294), we decided to conduct a full analysis on the mounted round brilliants in this bracelet.

Testing was first performed on the 60 near-colorless round brilliants with the DTC DiamondSure. Several samples were referred and sent for further testing using Raman spectroscopy. Of these, two round brilliants were suspected as imitation. Close examination under the optical microscope revealed obvious doubling on the facet junctions, a key identification feature for synthetic moissanites (K. Nassau et al., “Synthetic moissanite: A new diamond substitute,” Winter 1997 G&G, pp. 260–275). Further testing with Raman spectroscopy confirmed this identification with three peaks at 768, 789, and 966 cm–1 (figure 2).

Moissanite spectrum
Figure 2. Raman spectroscopy confirmed the identification of two colorless round brilliants as synthetic moissanite with peaks at 768, 789, and 966 cm–1.

FTIR spectroscopy performed on the other referred near-colorless and colored melee identified them as natural. One melee was found to be type IaB, while the others were type IaA.

This analysis showed that melee-sized diamond imitations are being mixed with natural diamond parcels and set into fine jewelry without proper disclosure. Therefore, proper identification by a gemological laboratory is an essential tool to maintaining the integrity of the industry.

Jessie Yixin Zhou is a staff gemologist at GIA’s New York laboratory.