“…The XRD patterns corroborate the SEM findings that show an intrinsically porous gypsum matrix that has some crystalline components (quartz and enstatite) and some calcite (CaCO 3 ) that could have accumulated due to water spraying during the thermal testing of the clay outlined in Section 4.4. The benefit of having gypsum in the composite is that it exhibits a retrograde solubility, or becomes less soluble at higher temperatures, adding to the stability of the porous structure [35,36]. The elemental analysis was also carried out using XRF, and the results are summarized in Table 2.…”