## 5 Results and Discussion
### Microstructure Analysis
Figure 6: SEM image of S1 sample showing (**a**) aggregates of pyrite forming framboids, and (**b**) pyrite crystals smaller than 1 \(\upmu\)m and (**c**) chemical composition of pyrite crystals smaller than 1 \(\upmu\)m given by the EDS spectrum. Impurities of other elements are attributed to broadened micro area composition (spot size of beam \(\sim\)5 \(\upmu\)m). The results of the plasticity limits were 15.50, 15.93 and 20.52 for samples 3, 6 and 1, respectively (Table 2). Therefore, according to the [PERSON] soils classification [50], all samples were characterized as high-plasticity soils. Samples of group 1 (S1, S2) were characterized through the presence of slightly higher amounts of phyllosilicates (50-52 wt%) and lower of non-phyllosilicate minerals compared to the other crystalline ones (48-50 wt%). Even though they do not contain pure smectite, which exhibits higher adsorption/absorption capacity and ion exchange ability among clay minerals, they contain significant amounts of mix layer chl-sm and pure vermiculite (26-28 wt%) clay minerals. Moreover, samples from group 1 consist of 24 wt% illite/muscovite, which further contributes to the hydration of dry skin [29]. Sometimes mica is altered to halloysite (mineral of the kaolinite group), as shown in Figure 7, which is not only biocompatible to normal human dermal fibroblasts, but also enhances the wound healing processes. A similar structure with halloysite minerals was also reported by [PERSON] et al. [51,52]. Using TEM analysis, the halloysite nanotubes that occupy a high surface area are observed, as can be seen in Figure 7b. In the literature, peloids usually contain low or minor amounts of carbonates [31]. However, the S1 and S2 specimens consist of significant micritic content (18-19 wt%), though it is not considered to act negatively. On the contrary, micritic calcite particles can act as a peeling constituent [31,53]. Previous researchers stated that using peloids with high amounts of nano silicon oxide and cristobalite should be avoided, since these phases are linked to silicosis phenomena or other diseases, such as carcinogenesis after exposure to silica dust [54, 55, 56]. On the contrary, the microcrystalline or amorphous quartz was shown not to be dangerous for human and pelotherapy, especially when this phase coexists with clay minerals [53,56]. In S1 and S2 samples, silicon oxide was largely found in the form of microcrystalline quartz (>100 nm in crystal size, Figure 8a), as well as in skeletons of diatom micro-organisms homogeneously dispersed in the matrix (Figure 8b,c); it was less common in nano crystalline quartz (<100 nm in size). The presence of diatoms improves the efficacy of peloids due to their thermophilic and anti-inflammatory properties [6], something that may remedy pain through reducing inflammation of the skin. In fact, the toxicity of silicon oxide phases in humans depends on multiple parameters (e.g concentration, use, time of exposure), and it is difficult to predict the effect. Nevertheless, it is recommended that this material is only used in mud paste form and removed when dry, avoiding harmful inhalation. Framboidal pyrite detected in these samples is not expected to influence the peloids behavior, since they occur in low amounts in texture microareas (lower to the XRD detection limit of about 2-3 wt%), whilst toxic trace element-free pyrite is used in cosmetics. It is reasonable to state that in the samples, toxic arsenic was detected in very low levels (Table 4), reflecting negligible release of such ions from pyrite crystals. Gypsum (2 wt%), feldspar (4-5 wt%) and dolomite (4 wt%) were detected in S1 and S2 as commonly presenting in peloids, doing so without changing their properties. Nevertheless, these minerals do not negatively affect human skin during the application