Abstract: The Clay Mineral Association and Environmental Significance of Ceshui Formation in Hunan Province一Clay minerals in Ceshui formation are cormposed mainly by kaolinite and illite, and secondarilv by a little of chlorite, pyrophyllite and illite-montmoril-lonite mixing layers. These minerals show regu lar. vertical variation, which. Corresponds to the evoluation of sedimentary environments.Illite and pyrophyllite are prevailing in lagoon and littoral shallow deposits. Koalinile and illite are respectively major and secondary clay minerals in fresh lagoon and swamp deposits.