Firing behaviour of the lower cretaceous clays of Tunisia

The Valangenian–Hauterivian clays of Tunisia located at Djebel Oust were characterised by chemical analysis, X-ray diffraction and scanning electron microscopy in order to determine if these clays are appropriate for the manufacturing of ceramic products for construction. The mineralogical study shows that these clays are mainly of illitic type. However, other clay minerals, such as kaolinite, I/Sm mixed-layer, and chlorite, are also present. The chemical analysis indicates that the clays are notably siliceous, carbonated and aluminous. The content of iron is variable. Under firing tests on clay raw material until 1200 °C, quartz, cristobalite, hematite, mullite and sillimanite minerals were also identified. The amount of interstratified I/Sm and chlorite is higher in the samples located at the west zone of Djebel Oust than those located at the east. However, under firing behaviour of both types of raw samples seems to be similar. As conclusion of this study, these clays meet the firing specifications required for the manufacturing of ceramic products for construction.