## 4 Conclusions  
Mine spoils with a high amount of illite create mullite at 995 \({}^{\circ}\)C. Cristobalite was not detected as a high-temperature phase. More or less significant amounts of amorphous material and glassy phase were detected in all fired samples (\(>\)45%). The higher percentages of mullite (18-8%) and vitreous phase (\(>\)55%) at 995 \({}^{\circ}\)C were due to the presence of an abundant amount of illite in all samples. At 1150 \({}^{\circ}\)C, the content of mullite in the fired OE selected samples (39%) was higher than the ones from the AA series (28%). Between 1050 and 1100 \({}^{\circ}\)C, there is an important decrease in the open porosity in AA fired samples. However, this behavior is not observed in the OE fired samples, where the open porosity increased between 1050 and 1100 \({}^{\circ}\)C. The role of the mullite in this behavior could be an area for future new research. Despite observing a porous microstructure, the non-porous areas are well sintered. The presence of quartz and amorphous phase were observed together with small scale-shaped crystals of mullite and hematite coatings forming crusts.  
Figure 5: Growth of minerals, and presence of abundant vitreous phase and low porosity in tile bodies fired at 1150 \({}^{\circ}\)C. (**A**) The presence of quartz and amorphous phase were observed together with small scale-shaped crystals of type I primary mullite (\(<\)0.2 \(\upmu\)m in size). (**B**) Crystallizations on the vitreous phase on the fracture surface. Hematite coatings are observed forming crusts.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & **T** & **VT** & **ST** & \(\varphi\) & \(\varphi_{app}\) & \(\varepsilon\) & **Kp.10–16** & _r.10–8_ \\  & **(\({}^{\circ}\)C)** & **(mL/g)** & **(m\({}^{2}\)/g)** & **(g/mL)** & **(g/mL)** & **(m)** & **(m)** \\ \hline \multirow{4}{*}{OE} & 995 & 0.142 & 2.09 & 1.895 & 2.603 & 0.375 & 8.72 & 13.44 \\  & 1050 & 0.074 & 1.78 & 2.186 & 2.577 & 0.180 & 1.59 & 8.22 \\  & 1100 & 0.135 & 2.29 & 1.944 & 2.601 & 0.344 & 6.01 & 11.97 \\  & 1150 & 0.030 & 1.684 & 2.243 & 2.480 & 0.083 & 0.06 & 5.98 \\ \hline \multirow{4}{*}{AA} & 995 & 0.143 & 3.505 & 1.919 & 2.668 & 0.285 & 2.43 & 8.40 \\  & 1050 & 0.100 & 1.917 & 2.125 & 2.696 & 0.222 & 3.25 & 10.40 \\ \cline{1-1}  & 1100 & 0.061 & 1.345 & 2.286 & 2.620 & 0.142 & 1.32 & 8.86 \\ \cline{1-1}  & 1150 & 0.038 & 1.745 & 2.352 & 2.581 & 0.092 & 0.25 & 4.33 \\ \hline \hline \end{tabular} Legend: T (temperature); VT (total Hg volume that penetrates into the pores); ST (specific surface); \(\varphi\) (density); \(\varphi_{app}\) (apparent density); \(\varepsilon\) (open porosity); Kip (coefficient of permeability); r (average pore radius).  
\end{table}
Table 5: Parameters that describe the porous texture of the ceramic tile bodies.  
**Author Contributions:** Conceptualization, M.M.J. and S.M.; methodology, M.M.J. and S.M.; software, S.M.; validation, S.M., F.P. and M.A.M.; formal analysis, S.M. and M.M.J.; investigation, M.M.J., S.M., M.A.M. and F.P.; writing--original draft preparation, M.M.J.; writing--review and editing, M.M.J.; supervision, M.M.J.; project administration, M.M.J. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research received no external funding.  
**Acknowledgments:** The authors would like to express their gratitude to [PERSON] for his help in the discussion and comments; and dedicate this manuscript to the memory of [PERSON], for his hard work in the study of Spanish ceramic clays.  
**Conflicts of Interest:** The authors declare no conflict of interest.