gems, turquoise, treated turquoise

Turquoise has undergone various treatments to enhance its value as a gem, such as improving color or reducing porosity, and numerous imitations also exist on the market. While many of these are still labeled as turquoise (Galia, 1977), the only true synthetic currently available is the so-called Gilson synthetic turquoise, which includes crystalline turquoise as a component. Differentiating natural, untreated turquoise from treated material—and clearly identifying imitations or synthetics—is challenging with routine gemological techniques. However, mineralogical methods such as X-ray powder diffraction and infrared spectroscopy can provide the necessary data to adequately characterize the material (Banerjee, 1972; Arnould and Poirot, 1975; Williams and Nassau, 1976–1977; Schmetzer and Bank, 1980, 1981).