The influence of self-generated gaseous products on the kinetics and mechanism of the thermal decomposition of synthetic malachite, Cu2CO3(OH)(2), was investigated by means of conventional TG-DTA under various atmospheric conditions, TG-MS and CRTA under a reduced atmospheric condition, and powder X-ray diffractometry of the partially decomposed sample. It was found that the sample decomposes at a lower temperature under a higher partial pressure of self-generated gases. This interesting behavior, in contrast to the general consideration of chemical equilibrium, results from catalytic action of evolved H2O on the crystallization of the product CuO, and from an interaction of evolved CO2 with poorly crystallized CuO under reduced pressure.