The possibility of forming magnesite from brucite crystallites, in a CO2-rich environment, has attracted large interest as a possible industrial procedure to store CO2 in the form of carbonate minerals. The reaction mechanisms responsible for such processes are, however, not very well-known. In this work we first consider the compatibility of the magnesite and brucite structures, along specific crystallographic directions. In the second part we describe the sequence of events that leads to the formation of a magnesite layer, via the dehydroxylation of brucite and consequent adsorption and diffusion of carbon complexes. To observe these thermally activated events, we employ a method recently developed in our group(1,2) for finding complex reaction pathways and reproducing the related free energy surface. We find that the (1100) brucite surface can be dehydroxylated quite easily. The formation of vacancies in the hydroxyl layers might favor the diffusion of OH and protons through the channels between two neighboring (0001) OH planes, which characterize the brucite structure. This mechanism creates the necessary conditions for further dehydroxylation and formation of magnesite layers.