Dickite is a phyllosilicate clay mineral, with the same composition as kaolinite, nacrite, and halloysite, but with a different crystal structure (polymorph).
Its chemical composition is Al2Si2O5(OH)4. It occurs with other clays and requires x-ray diffraction for its positive identification. Dickite is an important alteration indicator in hydrothermal systems as well as occurring in soils and shales. It takes its name from Allan Brugh Dick (1833-1926), the Scottish metallurgical chemist who first described it.