In order to fully dissolve the reaction mixture and the quartz impurities, we have studied the effect of temperature and time during the gel formation. Two steps are differentiated: the first one refers to the homogenization of the reaction mixture using magnetic agitation, and the second one involves the aging of the gel for certain period of time in static. These two processes were tested both at room temperature (RT) and 50 C for the two kaolins, R and P, at 3M and with further treatment at 100 C for 3 h. The results of crystallinity obtained from the quantitative measured XRD profiles are collected in Table 3. The gel formation at 50 C resulted in better crystallinity probably due to the complete dissolution of the metakaolin