A soft white day occurring in diverse types of are mineralization as lenses, cavity and veinlet fillings in the Rakos hydrothermal mercury deposit is shown by X-ray powder diffraction, SEM, thermal and chemical analyses to be essentially well ordered 1 Tc kaolinite, sub-ordinate dickite or mixture of both. These kaolin-group minerals crystallized from solutions and can be regarded as genetically associated with the youngest cinnabar mineralization.