Forensic Characterization of Nacre (Mother of Pearl) by pXRF and DRIFTS Analysis

This study aimed to develop non-destructive methodology to distinguish natural nacre (Mother of Pearl) from synthetic imitations, a task of growing importance due to increased demand and illegal trade. The research employed two key analytical techniques: portable X-ray fluorescence (pXRF) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Natural mollusk shells (n=50) and commercial synthetic Mother of Pearl products (n=18) were analyzed. The pXRF results revealed that natural nacre and faux nacre – composite materials containing synthetic and natural nacre parts – had higher relative concentrations of calcium (Ca) and strontium (Sr), with a distinct Ca/Sr ratio. In contrast, artificial samples lacked these elements and had a higher percentage of light elements (LE), indicating an organic, polymer-based composition. DRIFTS analysis characterized the molecular structure. Natural nacre spectra consistently showed peaks characteristic of aragonite, a crystalline form of calcium carbonate. While the synthetic samples, including the faux nacre composites, displayed spectra consistent with polymers like epoxy resin and acrylic. The findings confirmed that a combination of visual inspection for iridescence, pXRF elemental analysis, and DRIFTS analysis provides a robust approach for differentiating natural nacre from synthetic look-alikes. This method can assist in monitoring and combating the illegal trade of mollusk shells.