Chemical composition and structure of silicate minerals plays an important role in the obtaining of porous expanded clay materials. Perspective raw materials for such purpose in Latvia are local Devonian and Quarternary system clays. Content of illite (sheet silicate or phyllosilicate) as the main constituent of such claysvary between 50 and 80 % in Devonian clays and between 30 and 40 % in Quarternary clays. Fertiler clays are suitable for obtaining of expanded clay material, t.i. clays with higher content of typical clayey substance or from the viewpoint of grading composition – clays with higher content of particles with size < 0,005 mm, as well as lower content of sandy fraction and carbonates (CO2 – 6 % and less). Silicate minerals have to contain from the viewpoint of chemical composition gases and liquid phase development contributing ions - (OH)-, (H3O)+, H2O, Na+, K+, Fe2+, Fe3+ etc.