Abstract: The main types of volcanic rocks of the Yingcheng Formation in Santai area, southeastern uplift of the Songliao Basin are perlite, rhyolite, hydrothermal breccia, breccia conglomerate, tuff and so on. The devitrification of perlite and rhylolite is obvious. It can be found under microscope that the devitrification of perlite is of three phenomena: crystallite, skeletal crystal (microlite) and spherulitic while the devitrification of rhyolite is mainly of spherulitic. The development process of the devitrification is featured by a gradual increasing trend from crystallite to skeletal crystal (microlite) and finally to spherulitic. The formation and intensity of devitrification are related not only to the rock composition, but also to the formation and development of cracks. Laboratory tests indicate that the density of perlite, in the range of 3.13%-8.65%, is lighter after intense devitrification and is heavier with slight devitrification. Assuming a closed system, the decreasing density of rocks is corresponding to an increase in porosity of the rocks. Devitrification processes in the area can improve the reservoir properties of the glassy volcanic rocks.

Key words: Songliao Basin, Yingcheng Formation, devitrification, reservoir, perlite, rhyolite