# Structural Pattern Analysis in _Patella vulgata_ Shells Using Raman Imaging
## 1 Introduction
XRD provides the highly accurate and reliable identification of calcium carbonate polymorphs but is time-consuming and requires extensive sample preparation [26; 27]. SEM offers high-resolution imaging and detailed surface characterization; however, it does not directly determine material composition and operates under vacuum conditions [14; 28]. Elemental analysis techniques, mainly based on inductively coupled plasma mass spectrometry (ICP-MS), are inherently destructive, as they require the extraction of material along the shell growth axis. Laser-induced breakdown spectroscopy (LIBS), on the other hand, greatly simplifies sample preparation, but it is still quasi-destructive [29; 30; 31]. Stableisotope analysis offers valuable environmental and biomineralization insights, but it is time-consuming and has less spatial resolution [6; 32]. In archaeological research, where sample preservation is crucial, analytical techniques must balance resolution, efficiency, and non-destructive analysis. However, these methods often involve trade-offs between precision, resolution, and preservation, with the challenge of obtaining detailed compositional information while maintaining sample integrity. Raman spectroscopy is a non-destructive technique that allows for the characterization of both mineralogical and organic components in mollusk shells [20; 33; 34]. It is based on the inelastic scattering of monochromatic light, where molecular vibrations produce characteristic shifts in the scattered photons, enabling the precise identification of calcium carbonate polymorphs, trace elements, and organic compounds within the shell matrix [35]. Beyond single-point measurements, Raman spectroscopy enables the construction of high-resolution spectral maps, allowing the spatial characterization of compositional variations across different regions of the sample [36]. These maps can be applied to the study of biomineralization processes and the reconstruction of environmental conditions during shell formation [37]. Additionally, it requires minimal preparation, making it suitable for fragile or valuable specimens, particularly in paleontological and archaeological research. Raman spectroscopy is also compatible with portable devices, offering a versatile tool for in situ analysis, which is particularly valuable in field studies [38]. Recent studies have demonstrated the power of Raman imaging in biomineral research. [PERSON] et al. used Raman spectroscopy to investigate marine bioclification mechanisms in corals, providing insights into the role of amorphous calcium carbonate (ACC) precursors in skeletal growth [37]. [PERSON] et al. applied Raman mapping to the Antarctic clam _LaTe-nula elliptica_, revealing the coexistence of three calcium carbonate polymorphs (aragonite, calcite, and vaterite) within its shell [39]. [PERSON] et al. examined calcite-aragonite interfaces in _Haliotiis tuberculata_ using Raman and FTIR imaging, demonstrating the complexity of shell mineralization patterns and highlighting variations in mineral phase distribution between wild and farmed abalones [40]. Similarly, [PERSON] et al. employed Raman spectroscopy to analyze the shell composition of the limpet _Patella caerulea_, showing that individuals exposed to low-pH environments increase aragonite deposition to counteract dissolution [41]. [PERSON] et al. used Raman spectroscopy to map the spatial distribution of carotenoid pigments in the shell of _Arctica islandica_, revealing their presence not only on the surface but also within the growth layers, indicating a potential involvement in the biomineralization process [36]. These studies underscore the utility of Raman imaging for investigating shell biomineralization and environmental influences. This study applies Raman imaging to _P. vulgaris_ shells to investigate spatial variations in mineralogy, organic matrix distribution, and Mg incorporation.