Properties of sedimentary clays for Karatsu ware

Four sedimentary clays for Karatsu ware which were geologically derived from the weathered sandstone and granite were mined and used in this study. The chemical composition, mineral composition and morphology of minerals were investigated by XRF, XRD, SEM and TEM analysis. The mineral composition of normative α-quartz, feldspar and kaolin of two clays were 43.1, 4.7, and 44.3, and 52.1, 21.3, and 27.0, respectively. These clays had lower content of feldspar and higher content of kaolin than those of clays prepared from some sandstone for Karatsu ware. Average size of coarse particles in four clays was 22–28 µm and maximum particle size were 188–290 µm, and these sizes were similar to those of clays prepared from sandstone. It was suggested that the decomposition of feldspar to sericite and kaolin was promoted by the weathering and hydrolysis of sandstone or granite.