It has been shown that the Meraker-type microsilica with SiO2-content of ca. 98.5wt% behaves differently from other types of microsilica investigated earlier at our Institute since it does not follow the normal transformation sequence:microsilica --> cristobalite --> tridymitewhen it is heated at ca. 1000 degrees C. Due to the higher purity of this type of microsilica, it transforms directly either to quartz or cristobalite. However, if small amounts of Li2O were added to the microsilica, the following transitions could be observed by using DSC:low - tridymite -->(394 K) high - tridymite -->(444 K) upper high - tridymite