Firing transformations of Tertiary clays used in the manufacturing of ceramic tile bodies

The mineralogical transformations during the firing of six different raw materials used in ceramic tile manufacturing have been studied. Test samples have been prepared by extrusion and fired in the range of 800–1150°C. Analysis of the fired samples was carried out by X-ray diffraction (XRD). The presence of augite, gehlenite, hematite, spinel, wollastonite and abundant vitreous phase showed neomineralization. Mixtures of illitic clays containing abundant CaCO3 form gehlenite, wollastonite and anorthitic plagioclases above 950°C. Samples poor in CaCO3 give a simple mineralogical composition of quartz and hematite.