The rock kaolin exhibits wider diversity in genesis, texture, physical properties, and uses than probably any other common rock. Its diverse textures, shown in scanning electron micrographs, are correlative with, and indicative of genesis and industrial use of, kaolin. Kaolin originates by weathering, by hydrothermal alteration, or by crystallization from colloid-size sediment whose chemical composition is congruent with that of kaolinite.
Some kaolins freely slake into clay-sized particles when wetted with water and likewise develop natural plasticity; their texture is characterized by loosely expanded and packed crystals. Industrial uses of this type of kaolin exploit its free-slaking property.
Other kaolins, of diametrically opposite properties, do not slake and do not become plastic when immersed in water; their texture is one of compact, tightly interlocking crystals. They are appropriately used in industry where selected size, shape, and original bulk density in crushed clay particles must be maintained despite wetting.