Mullite crystallization was carried out by the inter-reaction of alternate layers of muscovite and kaolinite minerals. The nucleation and growth of mullite anisotropic crystals take place along the muscovite plane and specific structural relationships are observed, which confirm a topotactic effect with the high temperature form of muscovite. The [001](mull) axis is oriented parallel to [010](musc), [310](musc) axes. The mullite orientation is fully completed in a temperature range between the ternary eutectic at 985 degrees C and the ternary transition point at 1140 degrees C, of the SiO2-Al2O3-K2O system, which strongly suggests an influence of a small quantity of liquid phase at the interface. Along the kaolinite-muscovite interface, the realisation of highly textured ceramics can be achieved.