Ceramic properties of kaolinized tuffaceous rocks in Kesan region, Thrace, NW Turkey

The Kesan–Karlikoy kaolin occurrence is located in the SW Thrace (Turkey) and was formed by the alteration of tuffaceous rocks. The tuff and tuffaceous units are made up of (1) bentonite, (2) kaolin and (3) zeolite (mordenite-rich), from bottom to top. The 20–40 m thick kaolin level is beige, yellowish and whitish beige in color and sandy tuff in appearance. The alteration of the rock to kaolin was explained by chemical, optical and scanning electron microscope (OM and SEM) and X-ray diffraction (XRD) studies. In terms of mineral constituents, the samples were generally rich in kaolinite and quartz, and some of them contained minor amounts of smectite, feldspar, opal-CT and calcite as well. The kaolinite contents estimated by XRD-modal analysis range between 20 and 55 mass % in the kaolin zone. Representative sample from the kaolin zone was used for ceramic tests. Flexure strength and Young modulus were measured and porosity, bulk density and water absorption were determined. For the samples fired at 1140 °C, the flexure strength was 9.78 MPa. The elasticity modulus was 7.94 GPa. Water absorption and apparent porosity values were 12.7% and 22.9%, respectively. Finally, the apparent density was 2.33 g/cm3. Plasticity values of kaolin samples were also determined according to the Pfefferkorn plasticity test. The kaolinized tuff can be used for wall tiles, floor tiles, and tableware which are shaped by dry pressing and extrusion.