Synthesis of leucite crystals below 1000 degrees C using natural kaolin as the primary raw material was investigated. Spherical leucite crystals having a diameter of approximately 50 mu m were prepared by heating a powder mixture of Al-2(SO4)(3), kaolin and K2SO4 (in mass ratios of 3:3:15) at 900 degrees C for 3 h. Quartz, the main accessory phase in kaolin, and the amorphous metakaolin formed upon heating kaolin were found to be responsible for the decreased synthesis temperature. (C) 2005 Elsevier Ltd. All rights reserved.