Control over the crystallography, morphology and hierarchical assembly of crystals are important goals in advanced materials engineering with important application potential. Most studies hitherto have concentrated on using different templates for the controlled nucleation and growth of ceramic crystals. In this paper, we demonstrate the crystallization of barium sulfate within thermally evaporated aerosol OT (AOT) thin films by a process of Ba 2+ ion entrapment followed by SO42- ion entrapment. This process leads to the formation of flat, barite crystals in highly organized assemblies. The process of crystal assembly was found to be dependent on the composition of the host matrix. Contact angle measurements of the barite-AOT films indicated that they were hydrophobic, thus pointing to the role of hydrophobic interaction between the AOT monolayer-covered barite crystals in the assembly process.