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The thermal behaviour of Mg-rich clay minerals in two serpentinites was studied by means of DSC-TG, XRD, IR and SEM. Experiments are carried out heating at temperatures in the 600-1200 degrees C range for 2-4 hours. Analyses revealed that antigorite, talc and clinochlor are the main Mg-rich clay minerals. Dolomite and magnesite are accessory minerals. Chromite, magnetite and hematite are in small amounts. DSC-TG results of the antigorite rich sample reveal that most of the loss of free water and water absorbed at surface (approx. 13%) occurs at approximately 750 degrees C. The decomposition into the high-temperature products forsterite + enstatite proceeds via an intermediate assemblage of forsterite and a talc-like phase, observed within a temperature interval of 100+/-20 degrees C. The breakdown of antigorite and the talc-like phase is kinetically controlled by surface growth processes at the edges of grains. The decomposition of the talc-clinochlore-antigorite assemblage took place at higher temperature and produced enstatite and spinel. It is suggested that their formation dependents on how clinochlore dehydrates and on the talc trioctahedral arrangement, which provides rapid transformation into enstatite. The increase of the reaction rate with temperature is confirmed by XRD and IR data as well as by SEM. Results of this work, indicate that highly crystalline forsterite and enstatite form by dehydroxilation of Mg-rich minerals.