The formation of ceramic with the prevailing cordierite/mullite in the crystalline phase is greatly dependent on the raw materials used. In the present work the cordierite and mullite (or their solid – solutions accordingly with spinels and corundum) formation processes from compositions of natural raw materials (illite clay, dolomite) with synthetic additives (MgO, Al(OH)3, K2CO3) are studied. It is shown that the illite clay acts as a low viscosity liquid medium as well as a precursor for cordierite and mullite crystallisation in ceramics. The phase development using XRD – analysis and the SEM is studied. Particles size distribution of staiting powder and some properties of ceramic obtained are also demonstrated. It is shown that formation of the above mentioned phases starts at temperatures 1050-1080 0C and remarkably increases at 12000C for mullite and at 13000C – for cordierite.