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.