In this paper, we study the chemical and mineralogical composition of the Krasnoyarsk Kray clay used in the production of coarse ceramics. It is found that the fire –strength depends of method of preparation of clay paste. It is shown that the forced dissolution of the raw clay material effectively homogenizes clay paste. As a result, strength of the samples increased during firing. It is also justified by the influence of their mineralogical composition and there method of the preparation. It is proved that conditions of preparation and mineralogical composition affect equally.