Chalcedony beads coated with titanium nitride

Recently, RAG Gemological Laboratory in Turin received a necklace of unusual metallic appearance. The grayish gold chalcedony beads showed irregular surfaces that were actually small geodes with shiny and well-shaped crystals. The cavities in the beads were reminiscent of the small quartz-lined holes that are often formed in agates and chalcedony. The necklace consisted of 29 beads 12.0–12.5 mm in diameter, with a total weight of 84 g. Some loose beads allowed us to measure density. The value of 2.60 g/cm3 was in agreement with chalcedony. RI was not measurable on the opaque beads, and no fluorescence reaction was observed under long- or short-wave UV. A sawed bead revealed that the inner part consisted of light gray chalcedony without zonation. Observation of the area near the drill holes showed discoloration and the true color of the underlying material. The unusual color and reflectivity of the external surface, clearly not inherent to chalcedony, warranted investigations. The coating appears to be titanium nitride. identified with EDS low voltage analysisi and Raman spectroscopy