The effects of brine on recrystallization in halite are well known. However, properties of brine such as morphology, connectivity, diffusivity and the resulting influences on deformation mechanisms are still a matter of debate. This paper presents a microstructural study of dense, statically recrystallizing synthetic polycrystalline halite containing small amounts of brine. We used powders of two different grain size classes: <10 mum and 200-355 mum. The aggregates were compacted to brine-filled porosities less than about 2% and annealed at room temperature, without an external stress field. Coarse-grained samples undergo recrystallization manifested by the growth of large (up to 300 mum) strain-free grains into the deformed old grains. The new grains are frequently euhedral, with mobile grain boundaries moving at rates up to 6 nm/s. Their mobility is interpreted to be high due to the presence of water. Grain surfaces are smooth and the width of the water-rich zones is usually below the resolution of the SEM (less than 50 nm). The evolution of fine-grained samples starts with primary recrystallization and a reorganization of grain boundaries. After this stage, which lasts a few hours, normal grain growth effectively stops, and no significant increase of grain size is observed even after several months. Microstructural observations indicate contact healing at the grain boundaries, with dihedral angles ranging between 20 and 110degrees. We interpret these boundaries to be fluid-free, with the brine residing in a network of triple junction tubes. This system of triple junctions is interconnected and associated with significant permeability. While grain growth is inhibited in the fine-grained samples, after a few hours of annealing exaggerated grain growth is commonly initiated. This is manifested by the growth of large, euhedral grains replacing the fine-grained matrix. These grains also grow with low-index facets and their boundaries are also interpreted to be mobile due to the existence of a water-rich phase.
