# Physical-Chemical and Thermal Properties of Clays from Porto Santo Island, Portugal
## 4 Results and Discussion
### Chemical and Mineralogical Analysis
\begin{table}
\begin{tabular}{c c c c c c c c} \hline  & **5** & **14** & **14A** & **15A** & **26** & **36A** & **119** \\ \hline SiO\({}_{2}\) & 54.02 & 48.04 & 41.36 & 46.56 & 46.92 & 47.96 & 51.21 \\ TiO\({}_{2}\) & 1.93 & 2.88 & 2.04 & 2.88 & 2.40 & 2.60 & 2.10 \\ Al\({}_{2}\)O\({}_{3}\) & 17.65 & 16.13 & 12.52 & 16.22 & 16.40 & 15.65 & 16.31 \\ Fe\({}_{2}\)O\({}_{3}\) & 8.20 & 12.50 & 12.28 & 12.49 & 11.22 & 11.64 & 9.86 \\ MgO & 2.81 & 3.88 & 6.01 & 4.23 & 3.19 & 4.25 & 3.29 \\ CaO & 4.64 & 4.33 & 9.94 & 4.64 & 6.12 & 4.20 & 4.93 \\ Na\({}_{2}\)O & 2.62 & 1.57 & 1.69 & 1.78 & 1.97 & 1.59 & 2.62 \\ K\({}_{2}\)O & 0.92 & 1.03 & 1.25 & 0.82 & 1.53 & 0.81 & 0.83 \\ P\({}_{2}\)O\({}_{5}\) & 0.57 & 1.18 & 0.58 & 1.78 & 0.91 & 1.52 & 1.56 \\ SO\({}_{3}\) & 0.02 & 0.04 & 0.03 & 0.05 & 0.09 & 0.03 & 0.09 \\ LOI & 7.70 & 7.90 & 13.85 & 7.90 & 13.85 & 9.42 & 6.13 \\ CIA & 68.33 & 69.95 & 49.29 & 69.12 & 63.03 & 70.33 & 66.05 \\ \hline \end{tabular}
\end{table} 
Table 2: Chemical analyses (%) of major elements of residual soil samples from Porto Santo Island as well as Chemical Index Alteration (%). \begin{table}
\begin{tabular}{c c c c c c c c} \hline  & **5** & **14** & **14A** & **15A** & **26** & **36A** & **119** \\ \hline Smectite & 61 & 68 & 52 & 73 & 56 & 82 & 68 \\ Kaolinite & - & - & 3 & - & - & - & - \\ Plagioclases & 19 & 13 & 13 & 7 & 14 & 5 & 12 \\ K-Feldspars & 6 & 3 & 3 & 1 & 9 & 2 & 4 \\ Calcite & 3 & 3 & 17 & 2 & 2 & 2 & 3 \\ Hematite & - & - & 2 & - & - & - & - \\ Magnetite/maghemite & 5 & 10 & 4 & 6 & 11 & 9 & 6 \\ Opal & 6 & 3 & 6 & 6 & 6 & - & 7 \\ Anatase & - & - & - & 5 & - & - & - \\ Quartz & - & - & - & - & 2 & - & - \\ Smectite crystallinity & & & & & & & \\ index & 0.24 & 0.22 & 0.36 & 0.39 & 0.54 & 0.37 & 0.23 \\ d\({}_{060}\) & 1.50 & 1.50 & 1.52 & 1.50 & 1.49 & 1.50 & 1.49 \\ \hline \end{tabular}
\end{table} 
Table 3: Semi-quantification (%) and mineralogical qualification of residual soil samples from Porto Santo Island as well as crystallinity index and d060. In the study of the clay fraction (\(<\)2 \(\upmu\)m), through the appropriate treatments of orientated aggregates (natural, glycerol and 550 \({}^{\circ}\)C), minerals from the smectite group are the main components of residual soil samples from Porto Santo Island, with characteristic reflections between d\({}_{001}\) = 14.66 A and d\({}_{001}\) = 15.11 A. The crystallinity index, which reveals the structural order-disorder of smectite, was determined using the ratio between the width (measured at half height) and the height of reflection (001). Therefore, the smectite with the highest crystallinity (0.24, 0.22 and 0.23; Samples 5, 14 and 119, respectively) are those with the lowest values of this index (Table 3); these index values are lower (0.22-0.54) than those with the lowest values of the index (Table 3). Figure 3: XRD graphs of samples: (**a**) 14A and (**b**) 36A. than those studied by [PERSON] et al. [9] and [PERSON] et al. [39], which are, in first study, around 0.84, and in second one, between 0.13 and 1.61. The smectite from residual soil samples collected in this study displays a dioctahedral type, with d\({}_{060}\) values ranging from 1.48 A to 1.50 A, with the exception of Sample 14A, which displays a trioctahedral type (1.52 A) (Table 3). In addition, through the EDS analysis, it was possible to determine the presence of clay minerals from the smectite group, namely montmorillonite (Figure 4) and nontronite, with sodium (Na) being the main exchange cation, followed by calcium (Ca), magnesium (Mg) and potassium (K). Nearly twenty points were selected and analysed by SEM/EDS from each of the seven residual soil samples from Porto Santo Island. The most frequent chemical analyses by EDS are those shown in Table 4 (EDS1 and EDS2).