Two ways for practical use of illite clays were studied: chemical treatment and non-conventional application to promote sintering and formation of mullite –ZrO2 ceramics It is shown that treatment of the illite Quaternary clay by KOH leads to forming of the weakly connected illite structure. That results in significant decrease of sintering temperature of the obtained ceramic materials. Use of Devonian clay as additive 8 wt.% for mullite – ZrO2 ceramics leads to growth of its density and considerable increase of the compressive strength by maintenance of ZrO2 in tetragonal crystalline form.