Control over the crystallography and morphology of technologically important minerals is an important goal in the area of crystal engineering. Charged insoluble surfactant monolayers at the air-water interface (Langmuir monolayers) have proven to be popular mineralization templates. In this paper, we investigate the influence of trace quantities of alcohol (ethanol) in the aqueous subphase on the crystallography and morphology of BaSO4 crystals grown in the presence of anionic Langmuir monolayers at two largely different supersaturation ratios. It is observed that the crystals grow in the barite structure with interesting differences in morphology of the crystals grown with and without alcohol in the subphase. Preferential adsorption of ethanol molecules at the air-water interface is expected to influence not only the organization of the surfactant Langmuir monolayer but also to alter the dielectric properties of the interface and, consequently, the electrostatic binding of the ions with the Langmuir monolayer prior to mineralization.