Carbonate growth was examined within rock powders subjected to Marslike environmental simulations. Rates of growth under experimental conditions were 1012-1013 molecules cm-3 s-1 with or without an aqueous phase of H2O present and were found to be proportional to CO2 pressure, H2Oabundance, and particle surface area. Direct ultraviolet illumination of powders was found not to affect carbonate growth significantly, but photochemistry of absorbed H2O was though to play an important role in chemical alteration activity. Transitory damp periods induced in powders of some experiments by the melting of surface frosts were found to provide only slight assistance to the rate of growth in comparison with experiments in which sublimation of frosts occurred. Liquid water did, however, have a noticeable effect upon the distribution of carbonate material within experimental samples. On the basis of experimental results, carbonate formation is shown to be fully compatible with the low-pressure arid conditions characteristic of the present Mars surface environment. It is further concluded that carbonate formation is likely to be an important aspect of Martian chemical weathering, that carbonate material is likely to represent a major chemical reservoir for the outgassed CO2 inventory of Mars, and that in the absence of an aqueous phase of H2O in the environment this carbonate should form as submicron coatings on regolith particle grains.