Serpentine and Talc Crystal Chemistry Determined Non-destructively by Raman Spectroscopy

Combined Raman scattering and wavelength-dispersive electron microprobe (WD-EMP) analyses of series natural serpentine and talc samples, belonging to the collection of the Mineralogical Museum in Hamburg, demonstrate that Raman spectroscopy can be used for non-destructive and non-invasive quantification of elements within these minerals. In particular, the main objective of this research was to establish precise quantitative correlations between the presence of major (Mg) and minor (Fe and Mn) elements at specific crystallographic sites of these minerals and characteristic Raman peak parameters (peak positions, integrated intensities, and full widths at half maximum). This is based on the already established methodological approach in biotite-group minerals (Aspiotis et al., 2022). From the determined quantitative relationships, crucial in facilitating the non-invasive characterization of historical objects and geomaterials, the amount of Mg and (Fe²⁺+Mn²⁺) amounts in talc as well as Mg and Fe²⁺ in serpentines can be calculated with relative uncertainties that do not exceed 5%.

The effectiveness of this analytical methodology was successfully demonstrated through its application on valuable selected cultural-heritage artefacts belonging to the collections of Museum für Kunst und Gewerbe Hamburg (MKG), in particular on two Babylonian cylinder seals (example is given in Fig. 1) and two inscribed gems dated to the Late Antiquity (4^th-3^rd century BCE), where traditional sampling methods were unfeasible. As a result, it was shown that the determination of the crystal structure and chemical composition of serpentine and talc, which can be a marker of provenance, can be accomplished by Raman spectroscopy having the potential to be further applied in other cultural-heritage objects.