Kaolinitic materials from Romana (north-west Sardinia, Italy) and their ceramic properties

The Romana kaolins represent the alteration products of rhyolite-rhyodacite Oligocene volcanics from SW Sardinia, Italy. In order to assess their potentiality in the ceramic industry, samples from four prospects were analyzed from a chemical (XRF), mineralogical (XRD) and technological viewpoint. These raw materials basically consist of kaolinite+cristobalite+ quartz-tridymite-feldspars, with hematite and alunite restricted to certain zones or horizons. The kaolinite-to-silica minerals ratio varies to a large extent, affecting the technological properties of Romana kaolins, which are characterized by low values of shrinkage and bending strength after pressing, drying and firing. The behaviour during firing is quite refractory, with high water absorption even at high temperatures (1200-1300 degrees C). Overall, these kaolins could be used to manufacture vitrified tiles or sanitaryware; in both cases, the Sardinian raw materials should be added to the body in partial replacement of the quartz-rich kaolinitic clays currently used in the Italian ceramic industry.