## 4 Results and Discussion
### XRD Analysis  
The most representative XRD spectrum for the \"Noto\" stone is shown in Figure 3. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{2}{c}{**D**} & \multirow{2}{*}{**ACI**} & \multirow{2}{*}{**I\({}_{\alpha}\)**} \\  & **(nGy h\({}^{-1}\))** & & \\ \hline Noto stone & 14.9 & 0.06 & 0.07 \\ \hline Comiso stone & 22.4 & 0.08 & 0.11 \\ \hline Mendicino stone & 31.8 & 0.13 & 0.04 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The absorbed gamma dose rate (D), the activity concentration index (ACI), and the alpha index (I\({}_{\alpha}\)) for the investigated samples. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{2}{c}{**Activity Concentration**} \\ \cline{2-4}  & \(\mathbf{C_{Ra}}\) & \(\mathbf{C_{Th}}\) & \(\mathbf{C_{K}}\) \\  & **(Bq kg\({}^{-1}\))** & **(Bq kg\({}^{-1}\))** & **(Bq kg\({}^{-1}\))** \\ \hline Noto stone & 14.5 \(\pm\) 1.6 & 0.99 \(\pm\) 0.16 & 6.2 \(\pm\) 0.8 \\ \hline Comiso stone & 21.9 \(\pm\) 1.9 & 1.8 \(\pm\) 0.3 & 3.2 \(\pm\) 0.4 \\ \hline Mendicino stone & 8.6 \(\pm\) 0.7 & 9.4 \(\pm\) 0.8 & 169 \(\pm\) 23 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: \({}^{226}\)Ra, \({}^{232}\)Th, and \({}^{40}\)K average activity concentrations for analyzed natural stones. The crystalline mineral phases were determined by correlating the measured diffraction peak positions with the ICDD JCPDS database. The XRD spectrum reveals clear evidence of a dominant crystalline phase. The labeled peaks, all identified as calcite (Clt), highlight the presence of this mineral as the primary component in the sample. The most intense peak at approximately 29.5\({}^{\circ}\) 20, corresponding to the main reflection plane of calcite, indicates its high abundance. This condition is typical for calcite-dominated materials, as this peak is associated with the (104) plane, which produces the strongest reflection in calcite due to its crystallographic orientation. In addition, smaller but well-defined peaks are also observed between 20\({}^{\circ}\) and 70\({}^{\circ}\) 20, with characteristic positions confirming calcite as the only significant crystalline phase. These additional peaks further reinforce the conclusion that calcite is the principal mineral, and the uniform intensity and sharpness of these reflections suggest a highly ordered, well-crystallized structure. The lack of any notable peaks or secondary phases suggests that this sample is largely free from impurities, reinforcing the high purity of the calcite in the \"Noto\" natural stone. The uniformity of the diffraction peaks, coupled with the absence of significant noise, indicates that the sample likely has a homogenous structure without significant mineralogical variation. Thus, the XRD analysis strongly confirms that calcite is the only crystalline mineral present in the sample. The presence of sharp, well-defined peaks and the high intensity of the main calcite reflection identified a high-quality, well-crystallized stone with minimal impurities. The structural uniformity of the \"Noto\" stone make it more appreciated in architectural and ornamental applications, owing to its mechanical strength and visual appeal [53]. Moreover, Figure 4 reports the most representative XRD spectrum for the \"Comiso\" stone. Figure 3: XRD pattern of Noto specimen. Prominent peaks attributed to calcite mineral. The XRD pattern reveals two primary crystalline phases: calcite (Clt) and quartz (Qtz). Calcite is the predominant mineral, with its strongest diffraction peak occurring around 29.5\({}^{\circ}\) 20, corresponding to the (104) plane, indicating a high concentration of calcite. Multiple additional calcite peaks between 20\({}^{\circ}\) and 70\({}^{\circ}\) further confirm its dominance in the sample.