The influence of structured organic surfaces on the oriented overgrowth of inorganic crystals is a fundamental aspect of biomineralization. This paper describes the dramatic changes in the crystallization of calcium carbonate within thermally evaporated stearic acid films by varying the pH of the electrolyte solution. Reaction of CO2 with electrostatically entrapped Ca2+ ions within the lipid films leads to the in situ growth of CaCO3 crystals. Whereas crystallization at pH = 6 gave rise to calcite of rhombohedral morphology, crystals nucleated at pH = 3 of the electrolyte solution were discrete crystals of the metastable polymorph, vaterite, along with calcite exhibiting unusual morphology. The process of Ca2+ ion incorporation in the stearic acid matrix was followed by quartz crystal microgravimetry and Fourier transform infrared spectroscopy, while scanning electron microscopy and X-ray diffraction measurements were employed to study the morphology and orientation of the crystallites within the lipid bilayer stacks.