## 5 Results and Discussion
### Microstructure Analysis  
According to the macroscopic description of the geomaterials studied during the field study and drilling, they exhibited fine grain size textures and are classified as silt-clay materials. Laboratory analyses of studied samples indicated similar qualitative mineralogical compositions, while the predominate pelitic texture is also confirmed. The representative XRD analysis results are presented in Figures 4 and 5 and Table 2. They demonstrate that the samples mainly consisted of phyllosilicates, quartz, calcite, feldspars, pyrite, gypsum, dolomite and opaque minerals. Illite, vermiculite, chlorite and mixed-layers chlorite-smectite clay minerals were detected after clay fraction analyses (Figure 6). The majority of the minerals display clastic origin (e.g., quartz, feldspar, illite/muscovite) derived from the weathered rocks of the broaden area, while others, such as calcite, are clastic or authogenetic [46]. Pyrite appears in framboidal agglomerates (Figure 6a,b), which are formed after sulfate reduction and release of H\({}_{2}\)S. The last process can react to iron ions derived from detrital material during flood phenomena [47]. Since pyrite and other phases are usually found in small particles in the bond of the examined samples (\(<\)5 \(\upmu\)m of spot size), they prohibit accurate quantitative analyses via SEM; thus, only EDS spectra were selected to be presented as providing approximate stoichiometric (FeS\({}_{2}\)), while the other elements were attributed to the nearby micro region influence. Nevertheless, in this work, special care was taken to present phase analyses using the more suitable method of XRD analyses for these fine grain size materials. Additionally, quantitative mineral variations, especially in terms of samples derived from different areas, were detected (Table 3). This heterogeneity, especially in the amounts of phyllosilicate minerals, indicates that visitors who collect random specimens use material with rather different properties that obviously different results in each time. Since there are not standard official regulations about the mineral contents or element concentrations demanded in the natural materials used as peloids, our results are comparable to those in literature [29; 31; 48; 49] as well as to a commercial natural clay material used for cosmetic purposes (Reference sample named S0). In this way, a comparison between the Kefalonia material and materials that are on the market and/or were tested regarding their effectiveness is possible. Previous published studies revealed that the content of phyllosilicates in peloids, especially smectite, muscovite/illite and kaolinite, should exceed the 30-40 wt% of bulk composition [29; 48]. These minerals often exhibit low particle size and platy morphology, high surface area, high adsorption/absorption/moisture capacity, ion exchange ability and high thermal retention, while also being very soft with high plasticity after being mixed with water. These characteristics favor the easy coating of peloid paste on the skin, providing hydration or removing toxins and microbes from the skin, while they can offer nutritional ion metals with therapeutic benefits in human dermatitis, rheumatism etc. [30]. Natural materials from coastal areas, such as S1 and S2 (group 1), were used by the visitors of the island more frequently, since they are located near to the sea (Figure 2). Figure 4: Representative images of sampling areas: (a) S1, S2 samples; (b) S3, S4 samples; (c) S6, S7 samples. (d) Drilling for core sampling. (e) S5 core sample. Abbreviations: Cc, calcite; Dol, dolomite; Fsp, feldspar; Gyps, gypsum; Qz, quartz; CL, clay minerals. Figure 5: Representative diffractogram of the clay fraction of S1 sample. Abbreviations: Chl-Sm, mix-layer chlorite–smectite; I, illite; M, muscovite; V, vermiculite.