The mineralogical properties and formation process of kaolinite from the Iriki kaolin deposit were studies. The Hinckley indices of the kaolinite samples have the value between 1.06 and 1.75 indicating relatively ordered structure. The IR absorption frequencies related to Si-0 vibration shifted linearly with increasing degree of disorder. The electron microscopic observation suggested that the kaolinite was formed from smectite under hydrothermal conditions. The growth process of the kaolinite can be divided into two stages. The first stage is formation of irregular-shaped particles. The second stage is dissolution of the irregular-shaped particles and growth of hexagonal-shaped particles. This formation process is controlled by the Ostwald ripening mechanism.