Dolomite powder from Coin (Spain) was heated in air at a constant rate of 2degreesC/min to 1000degreesC, while neutron diffraction patterns were collected every 150 s. Rietveld refinement was applied and raw intensity data were used to monitor decomposition. The full process happened in two stages: dolomite decomposition to give calcite and periclase, and calcite breakup. The first stage activation energy was 47 kcal.mol(-1) from fitting to a contracting sphere model. The dolomite mean thermal expansion coefficients were (6.7 +/- 0.4) X 10(-6) and (2.7 0.2) x 10(-5) K-1 along the a and c axes, respectively. Changes in the Ca-O and Mg-O bond distances were also measured.