Color-Change Synthetic Cubic Zirconia as Peridot Imitation
Peridot is a common gemstone in the jewelry industry; however, it is rarely simulated using substances other than glass (Summer 2004 Lab Notes, p. 165). The State Gemological Centre of Ukraine recently received for identification an oval-cut gemstone, with an estimated weight of 4.50 ct, set in a ring. The stone was greenish yellow in daylight, as seen in the image on the left, and orangy yellow in incandescent light (right). The client who submitted the ring specifically wished to know if the center stone was peridot. The sample was transparent and isotropic, with a refractive index of 2.150 (measured by a refractive index meter) and was inert to both short-wave and long-wave UV radiation. Microscopic examination revealed no inclusions. The measured relative reflectivity (RR 65–67), obtained using a Presidium DuoTester, clearly matched that of cubic zirconia, a result in line with the other gemological observations. This allowed us to identify the stone as cubic zirconia. Chemical analysis with energy dispersive X-ray fluorescence (EDXRF) showed Zr and Y, with minor Pr and Nd. These impurities can cause color change in this stone. Using fiber-optic light with the spectroscope, we observed a complex set of absorption lines in both the orange and green-blue regions (the same measurement can be seen at http://www.gemlab.co.uk/peridot.html). This study shows the importance of studying a variety of simulants, even those for less-expensive gems such as peridot.