The Tasoluk kaolinite deposits of Afyonkarahisar (western Anatolia) are hosted by both pre-Early Cambrian sericitic mica-chlorite schists and Neogene volcanites, the later comprising tuffs and agglomerates. These units have been affected by hydrothermal alteration controlled by faults resulting in complex, irregular, lateral mineralogical zonation. The occurrence of a siliceous cap on altered schists and in claystone, of quartz veins in schists and tuffs, and the development of explosion cones and pit fillings indicate that alteration in both the schists and the volcanites is due to hydrothermal processes. Altered schists have generally large (locally small) Fe contents, and claystones are generally silicified and have small Fe Contents. Kaolinite predominates south and west are of Tasoluk, whereas high (Fe+Ti)-bearing illite + kaolinite predominate in other altered sections. The kaolinite exhibits a stacked micromorphology within altered schists, and the altered volcanites record in situ precipitation, derived from a mechanism of paired dissolution and precipitation. Illite fibres coexist with kaolinite, smectite, chlorite, mica and sericitized feldspar in markedly altered schists. revealing that the illite formed either authigenically or by conversion of smectite to illite. A relative increase in Cr+Ni and decrease ill Sr+Ba in the kaolinite deposits and their schistose host rock relative to the upper level of the kaolinite deposits and their volcanic parent rocks came about by the alteration of chlorite, mica and feldspar in the sericitic mica-chlorite schists, and feldspar, glass shards and schist fragments in the volcanites as a result of extensive faulting, fracturing and hydrothermal activity during Late Miocene-Pliocene volcanism, which contributed to the development of kaolinite deposits under acidic environmental conditions. With regard to industrial applications, the low-Fe kaolinized schists are suitable for use in refactories and paper coatings, while the claystone is suitable for use in ceramics and in the white-cement industry.