High-sulfur fuels, such as petroleum coke and high-sulfur coal, are associated with fouling caused by the sulfation process itself. Earlier work on calcitic limestones has suggested that such phenomena usually occur at high levels of sulfation (60% or more), and that inerts, such as silica, iron, and alumina compounds, in the fuel ash can reduce agglomeration. The situation with dolomitic limestones is less clear, and in particular the effects of the Mg component on this form of agglomeration requires study. This work shows that agglomerates from dolomites can develop strength in much the same way as those from calcitic limestones, and that a double-salt, CaMg2(SO4)(3) is probably involved in this strength development at lower temperatures. Its presence has been detected in mixtures of fine CaSO4/MgSO4 powder at temperatures at least up to 750 degreesC and in sulfated dolomite samples at 700 degreesC. However, it is also clear that, in the absence of the sulfation process, mixtures of CaSO4/MgSO4 do not develop significant strength under the test conditions associated with this work.