## 4 Results and Discussion
### Molecular/Mineralized Characterization  
\(\upmu\)-Raman spectroscopy was employed as a screening tool to confirm the presence of compounds previously hypothesized through \(\upmu\)-EDXRF, and to identify potential alteration products indicative of chemical weathering and degradation processes affecting the investigated stones. Figure 8 shows the \(\upmu\)-Raman spectra, and corresponding photomicrographs, collected on blackish (Figure 8a), translucent (Figure 8b), red (Figure 8c), and white (Figure 8d) areas of the SP1 sample. The spectrum acquired from the blackish area (Figure 8a) shows the characteristic bands of quartz (SiO\({}_{2}\)), centered at \(\sim\)130 cm\({}^{-1}\), \(\sim\)206 cm\({}^{-1}\), \(\sim\)262 cm\({}^{-1}\), \(\sim\)355 cm\({}^{-1}\), \(\sim\)395 cm\({}^{-1}\), \(\sim\)462 cm\({}^{-1}\), \(\sim\)806 cm\({}^{-1}\), and \(\sim\)1162 cm\({}^{-1}\), along with a minor contribution falling at \(\sim\)1083 cm\({}^{-1}\), ascribable to calcite, the most stable polymorph of calcium carbonate (CaCO\({}_{3}\)). This is consistent with an argillitic rock composed of silicate phases (including quartz, feldspar, and phyllosilicates) intermixed with carbonate components. Moreover, the \(\upmu\)-Raman analysis of the translucent area (Figure 8b) provided evidence of the presence of anatase (a metastable TiO\({}_{2}\) polymorph), through the detection of its major contribu  
Figure 7: \(\upmu\)-EDXRF maps for Ca, Si, Fe, Al, K, and Ti detected in the bulk matrix (cross-section, SP2/_bulk_) and external surface (SP2/_surf_) of SP2. The rainbow color scale relates to the intensity of the main XRF transition line of the corresponding element. tion centered at ~144 cm\({}^{-1}\) and a minor feature at ~638 cm\({}^{-1}\), in conjunction with calcite (~1085 cm\({}^{-1}\)). The presence of anatase, often associated with low-temperature oxidizing conditions, typical of burial environments, can be considered to be a weathering product likely derived from the alteration of Ti-bearing minerals. In contrast, the \(\upmu\)-Raman spectrum (Figure 8c) acquired from the red area reveals all of the Raman features of rutile, the thermodynamically stable TiO\({}_{2}\) polymorph, at ~147 cm\({}^{-1}\), ~240 cm\({}^{-1}\), ~452 cm\({}^{-1}\), and ~615 cm\({}^{-1}\)[61]. Ratile is commonly present as a primary accessory mineral in metamorphic and igneous rocks, typically forming reddish-brown inclusions or fine-grained aggregates [62]. The simultaneous presence of anatase and rutile can be reasonably explained by their distinct origin: rutile as a relict sedimentary component, and anatase as a secondary weathering phase. A direct transformation of rutile to anatase is unlikely, due to their different thermodynamic stabilities [63]. Finally, in the \(\upmu\)-Raman spectrum of the white area (Figure 8d), collected on a white crust of the surface, the presence of calcite and anatase can be distinguished, together with aluminosilicates (i.e., feldspar or kaolinite) and calcium oxalates (i.e., whewellite or weddellite) from the broad bands between 1200 and 1800 cm\({}^{-1}\)[64; 65]. Interestingly, in all of the investigated areas, no signals related to gypsum (CaSO\({}_{4}\):2H\({}_{2}\)O) were observed, indicating that the SP1 argillite sample has not been affected by sulfate-related weathering or by severe exposure to sulfate-rich environments (e.g., coastal areas) [66]. Figure 8: \(\upmu\)-Raman spectra, and corresponding photomicrographs, collected on (**a**) blackish, (**b**) translucent, (**c**) red, and (**d**) white areas of the SP1 sample. The Raman spectra of the SP2 sample closely resemble those of SP1, indicating a similar molecular composition between the two samples. The XRD analysis fully corroborated and expanded the findings obtained through \(\mu\)-Raman spectroscopy.