Lightweight glass-ceramic material similar to foam glass was obtained at 700 degrees C-800 degrees C directly from alkali-activated silica clay and zeolitized tuff without preliminary glass preparation. It was characterized by low bulk density of 100-250kg/m3 and high pore size homogeneity. Chemical processes occurring in alkali-activated silica clay and zeolitized tuff were studied using X-ray diffraction, thermal gravimetry, IR-spectroscopy, and scanning electron microscopy. Pore formation in both compositions is caused by dehydration of hydrated sodium polysilicates (Na2O center dot mSiO2 center dot nH2O), formed during alkali activation. Additional pore-forming gas source in alkali-activated zeolitized tuff is trona, Na3(CO3)(HCO3)center dot 2H2O, formed during interaction between unbound NaOH and CO2 and H2O from air. Influence of mechanical activation of raw materials on chemical processes occurring in alkaline compositions was also studied.