Common Types of Turquoise Imitations in the Market and Their Identification Characteristics

This study focused on the representative turquoise imitations identified in recent years by the Jewelry Testing Laboratory of Guangdong Zhuhai Supervision Testing Institute of Quality and Metrology. The types of turquoise imitations circulating in the Zhuhai jewelry market were systematically investigated, and the identification features of natural turquoise, treated turquoise, and their imitations were compared. Conventional gemmological methods combined with infrared spectroscopy (IR), ultraviolet-visible (UV-Vis) spectroscopy, scanning electron microscopy (SEM), and X-ray powder diffraction (XRD) were used for the investigation. The results showed that the hydroxyl absorption peaks at 3 503 cm^-1 and 3 460 cm^-1 in the IR spectrum serve as key indicators for distinguishing natural turquoise from imitations. Peaks of IR spectrum at 1 734 cm^-1 and 2 855 cm^-1, or at 1 510 cm^-1 and 1 611 cm^-1, indicate the presence of filler treatment. In UV-Vis spectroscopy, the absence of the characteristic absorption peak at 427 nm or the appearance of a broad absorption band around 680 nm can be used as auxiliary evidence for dyeing. SEM observation reveals that the micro-morphology of imitations is significantly different from the platy or layered growth structure of natural turquoise. For compositionally complex imitations, such as barite-cemented composites or barium feldspar ceramics, XRD is essential for accurate identification. This study provides practical technical guidance for the accurate identification of turquoise and contributes to standardize market practices.