When compared with the parameters that indicate the pozzolanic activity, the compressive strength of the geopolymeric paste prepared with dacitetuff calcined at700°C attains thehighest value equal to 42.5 MPa at the usual curing temperature of 40°C (Figs. 5 and 6). This is thought to be the result of activation of the zeolite, which converts from clinoptilolite to mordenite at 700°C. Continued heat treatment up to 800°C converts mordenite to opal, which reacts strongly with alkaline solutions and gives a compressive strength of 68.5 MPa when cured at 20°C, 37.6 MPa at 40°C, and 60.4 MPa at 80°C curing. However, with untreated Shahindej dacite, the strength of the geopolymeric paste varies from 22 MPa at 40°C to 81.55 MPa at 80°C because of the elevating curing temperature (Figs. 5 and 6). The 900°C samples mostly show the lowest strength as a result of deactivation, depending on the specific surface area and soluble fraction decrease and the crystalline increase (Figs. 5 and 6).