# Physical-Chemical and Thermal Properties of Clays from Porto Santo Island, Portugal
## 4 Results and Discussion
### Chemical and Mineralogical Analysis
These two examples describe two clay minerals from the smectite group and are represented by the following crystallochemical formula:  
EDS1--(Si\({}_{3.7}\)Al\({}_{0.3}\))(Al\({}_{1.3}\)Fe\({}_{0.1}\)Mg\({}_{0.6}\))(Ca\({}_{0.1}\)Na\({}_{0.7}\))O\({}_{10}\)(OH)\({}_{2}\)(H\({}_{2}\)O) can be considered as montmorillonite. EDS2--(Si\({}_{2.9}\)Ti\({}_{0.3}\)Al\({}_{0.8}\))(Al\({}_{0.3}\)Fe\({}_{1.5}\)Mg\({}_{0.2}\))(Ca\({}_{0.3}\)Na\({}_{0.2}\)K\({}_{0.1}\))O\({}_{10}\)(OH)\({}_{2}\)(H\({}_{2}\)O) can be considered as nontronite. As can be seen in the crystallochemical formula of smectite, despite montmorillonite containing a low iron (Fe) content, it is rich in aluminium (Al) and magnesium (Mg); on the other hand, nontronite contains a significant content of iron in the octahedral layer. The residual soil samples from Porto Santo Island show higher concentrations of Ba (barium), Cr (chromium), Cu (copper), Mn (manganese), Ni (nickel), V (vanadium) and Zn (zinc) compared to the other minor and trace elements (Table 5). These concentrations vary between 46 and 177 ppm in Ba, 5 and 57 ppm in Cr, 8 and 70 ppm in Cu, 572 and 3900 ppm in Mn, 4 and 114 ppm in Ni, 4 and 177 ppm in V and 86 and 108 ppm in Zn, which is in line with [PERSON] et al. [23]. According to [PERSON] et al. [23], the higher concentration was obtained for Ba (504 ppm), Cr (79 ppm), Cu (90 ppm), V (188 ppm) and Zn (99 ppm) and can be associated with the bedrock and chemical element mobility [30; 42]. In agreement with the United States Pharmacopeia (USP 40-NF 35) [43], these elements, except for Ba and Zn, are classified as \"Class 2\" in terms of toxicity level, and it is recommended that their concentrations do not exceed the accepted limits. Therefore, according to the U.S. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline  & **Al** & **Ca** & **Cl** & **Fe** & **Mg** & **O** & **K** & **Si** & **Na** & **Ti** \\ \hline EDS1 & 4.7 & 0.4 & 0.0 & 0.4 & 1.8 & 79.0 & 0.1 & 11.5 & 2.1 & 0.1 \\  & & & & (Si\({}_{3.7}\)Al\({}_{0.3}\))(Al\({}_{1.3}\)Fe\({}_{0.1}\)Mg\({}_{0.6}\))(Ca\({}_{0.1}\)Na\({}_{0.7}\))O\({}_{10}\)(OH)\({}_{2}\)(H\({}_{2}\)O) & & & & \\ \hline EDS2 & 7.0 & 1.9 & 0.2 & 10.4 & 1.3 & 54.5 & 1.0 & 19.8 & 1.6 & 2.3 \\  & & & & (Si\({}_{2.9}\)Ti\({}_{0.3}\)Al\({}_{0.8}\))(Al\({}_{0.3}\)Fe\({}_{1.5}\)Mg\({}_{0.2}\))(Ca\({}_{0.3}\)Na\({}_{0.2}\)K\({}_{0.1}\))O\({}_{10}\)(OH)\({}_{2}\)(H\({}_{2}\)O) & & & & \\ \hline \end{tabular}
\end{table} 
Table 4: EDS analysis of two fine particles (1 and 2). Figure 4: Photography of a fine particle (<2 μm) of montmorillonite (ampliation 150\(\times\) and resolution 15 keV). Pharmacopeia, a set of standards and methods is needed to guarantee the quality of raw materials, medicine drugs and other substances for curative usage [44]. Health Canada [45], the European Commission (EC No. 1223/2009) [46] and the European Medicine Agency (EMEA) [47] (Table 5) established the accepted limits that these elements must not exceed in order for them to be viable for therapeutic purposes. According to Health Canada [45], Ba has a maximum limit of 1300 ppm. Moreover, in line with the EMEA [47], the maximum limit for Cr is 25 ppm, for Cu is 250 ppm, for Mn is 250 ppm, for Ni is 25 ppm, for V is 25 ppm and for Zn is 1300 ppm. However, the chemical composition of residual soil samples can contain impurities that are harmful to health, known as potentially toxic elements (PTEs): antimony (Sb), arsenic (As), cadmium (Cd), mercury (Hg) and lead (Pb), among others [48] and references therein], which are classified as \"Class 1\" in terms of toxicity level [43]. These elements commonly appear in the chemical composition of clay materials because they occur in nature, but they can also result from anthropogenic causes such as car traffic, agricultural production or mining activity [49]. Among other problems, the PTEs can cause breast cancer and pancreatic cancer, respectively [50]. For this reason, the European Commission [46] developed a list of substances prohibited in cosmetic products (EC No.