A method based on the analysis of the temperature profiles is proposed to identify changes in the physical structure and/or in the chemical composition of a solid when a constant heat flow passes through it. This analysis is applied to natural carbonates which are important from an industrial point of view. The thermal conductivity of the calcined and non-calcined naturals carbonates is determined in order to I elate variations in the temperature profiles with changes in the structure of the solids under study. A mathematical model, which predicts temperature profiles in spherical samples for heat transport processes similar to those studied, is proposed. This model is able to predict temperature profiles in heat transport processes, with or without chemical reaction, and with the chemical reaction fitting the progressive conversion model or the unreacted core one.