a finely crystalline form of hydrated aluminium silicate ... occurring as minute monoclinic flaky crystals with a perfect basal cleavage; resulting chiefly from the alteration of feldspars under conditions of hydrothermal or pneumatolytic metamorphism, or by weathering. The kaolinite group of clay minerals includes the polymorphs dickite and nacrite., savimineraal, kaoliini peamine koostisosa
