Microstructural characterization of varieties of serpentine group minerals in natural heterogeneous samples using Raman spectroscopy – A case study from the Erzgebirge (Saxony, Germany)

Serpentinites, formed through hydration of ultramafic rocks, have long been known to play a pivotal role in rock-water interaction accompanying plate-tectonic processes along divergent and convergent margins. Lately, they have attracted growing geoscientific interest due to their role in hydrogen generation and carbon sequestration by mineral carbonation. Serpentine group minerals, as their main constituents, occur naturally in three main varieties: antigorite, lizardite, and chrysotile. Traditionally identified by X-ray diffraction (XRD) and electron microscopy, homogeneous serpentines can also be effectively distinguished using Raman spectroscopy based on characteristic spectra. A critical question remains: Can Raman spectroscopy offer clear identification of serpentine varieties in natural, heterogeneous serpentinites?

For this study we applied Raman spectroscopy to serpentinites from Zöblitz in the Erzgebirge (Saxony). The serpentinites are hosted in quartzofeldspathic gneisses that underwent high-pressure metamorphism during the Variscan orogeny. They show a range of macroscopic textures, from garnet-bearing, highly serpentinized peridotites with isotropic matrices to decimeter-scale banded serpentinites. Raman spectra were collected through spatial mapping both in low (200–1350 cm⁻¹) and high (3200–3950 cm⁻¹) wavenumber regions on polished thin sections. The mapped areas were also examined using polarization microscopy.

Data processing involved analyzing peak parameters (peak position, full width at half maximum) and comparing spectra to reference data using classical least squares (CLS) fitting. The domains investigated, pre-characterized by polarization microscopy, showed clear microstructural heterogeneities linked to optical and morphological differences, all reflected in distinct Raman spectra. Comparing characteristic peak parameters, CLS fitting, and polarization microscopy enabled confident identification of the main serpentine varieties.