rock alteration leading to the formation of kaolin by the transformation of various minerals containing alumina, and, above all, of feldspars and mica. Kaolinization is most strongly manifested in the formation of a kaolin weathering mantle as a result of weathering in granites, syenites, and other feldspathic rock, evidently under humid, subtropical conditions. In this process a finely flaked, alumina-rich mica is initially formed from the feldspar. This mica is called sericite, and subsequently it becomes hydrated and is converted into hydromica and kaolinite. Remnants of hydromica are often present among the kaolinites that have formed as a result of kaolinization. Kaolinization processes are also manifested when there is perisurface hydrothermal alteration of rock in areas of volcanic activity.

Intensive processes of rock kaolinization and the formation ofweathering mantles occurred during the Carboniferous, Jurassic, Paleogene, and Neocene periods, which were characterized byabundant vegetation and a relatively humid and warm climate. Modern kaolinization is most characteristic in the humid tropics.