[en] The dissolution of single crystal and polycrystalline pollucite (Cs²O.Al²O³.4SiO²) has been investigated under static and Soxhlet conditions. Polycrystalline ceramics were prepared from a commercial pollucite powder by sintering at 1100₀C, 1200₀C and 1300₀C, and also by hot isostatic pressing (hip) at 1200₀C. The static tests were run at 40₀C and 90₀C in water (for up to 183 days) and in brine and silicate solutions (for 28 days). The solutions were analyzed with DC-plasma emission and the leached surfaces were examined with scanning electron microscopy (SEM) and other surface analysis techniques. It is concluded that the dissolution of polycrystalline pollucite is due largely to the preferential release of the glassy phase constituents since the single crystal studies verify the insolubility of the pollucite grains at near-neutral pH under static conditions. The dissolution behavior of polycrystalline pollucite under static and Soxhlet conditions is drastically different. Under static conditions, the pollucite grains are in equilibrium with the solution and the dissolved species originate only from the glassy phase. The glassy phase is more prevalent and has a higher Cs²O content in the denser ceramics sintered at 1200₀C; thus, the denser ceramics exhibit higher Cs leach rates. Under Soxhlet conditions the leach rates are linear and proportional to the specific surface area. Thus, the glassy phase is depleted from the surface region of the ceramics very rapidly, and the congruent dissolution of the pollucite grain continues at a linear rate. The Cs leach rates were highest in water, and lowest in the brine solution. 1 table