## 5 Results and Discussion
### Microstructure Analysis
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Sample** & & & & & & & \\ \hline  & **V, Sm,** & & & & & & \\  & **Chl-Sm, Chl** & **M/I** & **Fsp** & **Gyps** & **Cc** & **Dol** & **Qz** \\ \hline S1 & 28 & 24 & 5 & 2 & 18 & 4 & 18 \\ S2 & 26 & 24 & 4 & 2 & 19 & 4 & 21 \\ S3 & 13 & 10 & 7 & - & 35 & 4 & 31 \\ S4 & 12 & 12 & 6 & - & 35 & 4 & 31 \\ S5 & 13 & 12 & 9 & 7 & 24 & 4 & 31 \\ S6 & 16 & 10 & 6 & 5 & 29 & 5 & 29 \\ S7 & 10 & 9 & 8 & 3 & 27 & 13 & 32 \\ S0 & 12 & 30 & 8 & - & 18 & 6 & 26 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Semi quantitative mineralogical compositions of studied samples. Abbreviations: Cc, calcite; Chl–Sm, mix layer chlorite–smectite; Dol, dolomite; Fsp, feldspar; Gyps, gypsum; I, illite; Sm, smectite; V, vermiculite; Qz, quartz. of peloid paste due to their low amounts of toxic trace elements compared to harmless composition and low-to-moderate hardness (2-6 in Mohs scale). Samples of group 2 (S3, S4) present dense and fine textures, with low amounts of clay minerals (23-24 wt%) in their bulk composition compared to group 1 and commercial samples (S0). Moreover, this group could be characterized through the presence of increased percentages of quartz (31 wt%) and calcite (35 wt%) (Table 3). A lower amount of clay minerals in their bulk composition downgrades their efficiency in cosmetic or other therapeutic applications. Clay minerals of smectite group are lacking from their matrix since illite/muscovite coexist with vermiculite or chlorite. Diatoms are absent or occur seldomly. Additionally, since the distribution of quartz grains in the microstructure increases, the possibility of undesirable skin abrasion due to their high hardness (7 in Mohs scale) also increases. Thus, this fact was one of the parallel reasons for studying the materials of this region, which are widely used by numerous of tourists each year. These samples are also differentiated from the other peloids in the literature [53], as well as the S0 sample that was analyzed in this study (Table 3), which acted as the standard sample. Based on the bulk mineralogical composition criterion, earth materials at Xi beach similar to those of group 2 did not cover basic requirements and are not proposed for pelotherapy, as they do not present any of the necessary clay minerals required to improve or heal skin conditions. On the other hand, the samples of group 3 (S6, S7) that were collected farthest from the sea contained intermediate amounts of phyllosilicates (19-26 wt%) compared to the other samples, followed by lower amounts of quartz (29-32 wt%), calcite (27-29 wt%), feldspars (6-8 wt%), dolomite (5-13 wt%) and gypsum (3-5 wt%). Regarding the core sample (S5), petrographic features do not differentiate it strongly from the respect surface samples (samples of group 2 and 3, Table 3), confirming the extension of the in-depth studied horizon. Based on the aforementioned results, it is obvious that the clay fraction in the studied samples is significantly varied (it ranges between 19 and 52%), revealing the necessity for further investigation in this area and more systematic sampling in order to delineate micro-areas that could be used for pelotherapy in the future. Figure 7: (**a**) SEM image of S2 sample probably showing muscovite partially altered at edge of halloysite nanotubes (shown by the blue arrow); (**b**) TEM image of a probable halloysite nanotube of S2 sample, scale bar = 50 \(\upmu\)m.