The compositional join muscovite˗pyrophyllite at moderate pressures and temperatures

An investigation of compositions between muscovite, KAl₃Si₃O₁₀ (OH)₂ and pyrophyllite Al₂Si₄O₁₀ (OH)₂ was undertaken under hydrothermal conditions of 1, 2 and 3,5 kilobars water pressure and temperatures between 250° C and 440° C. The resulting five silicate phases were identified by X-ray diffraction, electron microscope and cation exchange capacity methods. The study permits the determination of the stability of expandable and mixed-layered phases under various physical and chemical conditions. A brief discussion of possible applications to natural mineral assemblages is made.