## 4 Results and Discussion  
### \(\mu\)-EDXRF Analysis  
Table 1 presents the average elemental composition obtained through \(\mu\)-EDXRF analysis for both the bulk matrix and the external surface of the SP1 and SP2 stone samples. Both SP1 and SP2 showed a similar elemental composition in their bulk matrix (i.e., SP1/_bulk_ and SP2/_bulk_), with a predominant calcareous phase, as indicated by the high Ca content (79.77 wt.% for SP1/_bulk_ and 71.74 wt.% for SP2/_bulk_). For these areas, significant amounts of Si (i.e., approximately 12 wt.%), Fe (i.e., approximately 5 wt.%), and Al (i.e., approximately 3.6 wt.%) were also detected, in conjunction with traces of other elements, such as Ti, Mn, Mg, Cr, Ni, Rb, Sr, S, Cu, and Zn (for which a wt.% < 1 was observed). As a  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c c c} \hline \hline
**Sample ID** & **Si** & **Ti** & **Al** & **Fe** & **Mn** & **Mg** & **Ca** & **K** & **P** & **Cr** & **Ni** & **Rb** & **Sr** & **S** & **Cu** & **Zn** \\ \hline \multirow{2}{*}{**SP1/_bulk_} & 10.80 & 0.53 & 2.98 & 3.90 & 0.45 & 0.28 & 79.27 & 0.58 & & 0.01 & 0.02 & 0.01 & 0.58 & 0.06 & 0.01 & 0.03 \\  & \(\pm\) & \(\pm\) & \(\pm\) & \(\pm\) & \(\pm\) & \(\pm\) & \(\pm\) & \(\pm\) & \(\pm\) & \(\pm\) & \(\pm\) & \(\pm\) & \(\pm\) & \(\pm\) & \(\pm\) & \(\pm\) & \(\pm\) & \(\pm\) \\  & 0.04 & 0.  
general consideration, the comparable wt.% values, especially those associated with trace elements, indicate that the stone used in the construction of the Sanctuary of Apollo (SP1) may have been sourced from the natural argillite bed represented by SP2. Interestingly, the slight differences in Ca content observed between SP1/_bulk_ and SP2/_bulk_ can be reasonably attributed to diagenetic recrystallization and soil-stone interactions, in agreement with the literature [59, 60]. These processes likely occurred at different rates due to variations in environmental conditions between the two sampling locations. Furthermore, the simultaneous detection of high amounts of Si, Fe, and Al is likely related to the presence of silicate and clay minerals in the stone matrix, such as quartz and aluminosilicates. A comparison of the elemental compositions between the bulk and the external surface of both SP1 and SP2 provided insights into the potential degradation processes affecting the investigated stones. First of all, a significant decrease in Ca content was observed on the external surface of SP1/_surf_ (55.67 wt.%) compared to its bulk matrix (79.77 wt.%), suggesting surface decay or leaching due to environmental phenomena. In contrast, the bedrock SP2 sample showed minimal differences between its surface and bulk matrix, indicating a stable carbonate composition with negligible leaching. Interestingly, the notable increase in Si and Fe contents from the bulk (SP1/_bulk_) to the surface (SP1/_surf_) likely reflects the presence, on the external surface of the stone, of insoluble residue-rich grains of both silicate and oxide types. Such a pattern was not observed in SP2, where the elemental composition remained consistent between the bulk and the surface, indicating limited surface alteration. The sulfur content on the external surfaces of SP1 (0.07 wt.%) and SP2 (0.03 wt.%) was comparable to their respective bulk compositions, reasonably excluding the presence of sulfation from environmental exposure. This aspect is corroborated by the absence of gypsum (CaSO\({}_{4}\) 2H\({}_{2}\)O), which would result from sulfuric acid-calcite reactions, as confirmed both by molecular characterization and ion chromatography, as discussed later in the text. \(\mu\)-EDXRF elemental maps enabled us to highlight the distribution of the major and some trace elements. Figure 6 displays the \(\mu\)-EDXRF distribution maps of some main elements (Ca, Si, Fe, Al, K, and Ti) present in the bulk matrix (SP1/_bulk_) and over the external surface (SP1/_surf_) of the SP1 sample.