The grain-scale properties of solid reactants have not previously been considered in relation to the overall kinetics of gas-solid reactions and an understanding of these relations may have an important role to play in the optimisation of industrial scale processes. In this X-ray m-CT study we have tracked the translations (up to 24 mm) and rotations (up to 0.6°) of ~ 600,000 individual calcite grains in a small sample of Carrara Marble (Michelangelo’s favourite) as it reacted with a stream of high temperature SO2-gas to produce calcium sulphate. Limestone sulphation is one of the key processes used for the industrial-scale removal of SO2 from flue gases discharging into the atmosphere to mitigate the problems of acid rain and ozone depletion. Using a combination of high-resolution SEM and X-ray CT technologies on a sequence of experimentally reacted marble discs and cylinders, we have also shown how sulphation reactions in carbonate aggregate material (commonly limestone) are initiated by non-anisotropic expansion of calcite grains and how individual grains become free to move with respect to each other as the sulphation reaction proceeds. Such grain kinematics maintain gas phase permeability while porous anhydrite develops as a continuum along all grain boundaries.