Magnesium-bearing calcium carbonate films have been synthesized via a polymer-induced liquid-precursor (PILP) mineralization process. A variety of morphological features of biominerals can be mimicked with this PILP process; therefore, our group has proposed that this crystallization system can be used as an effective in vitro model system for examining mechanistic issues related to biomineralization. Here, the effect of the Mg2+ /Ca2+ ratio on the rate of transformation of the amorphous precursor films was investigated using polarized optical microscopy (POM), and the final crystalline structure and composition were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), inductively coupled plasma spectroscopy (ICP) and energy dispersive spectroscopy (EDS). The entrapment of high levels of magnesium in the deposited precursor films had a pronounced inhibitory effect on the amorphous to crystalline transformation, and furthermore, influenced the polycrystalline nature of the film. The magnesium content incorporated within the calcite lattice (8-26%) resembles the range found in biologically formed high magnesium-bearing calcite, while much lower levels were formed via the conventional solution crystallization process. The formation of non-equilibrium morphologies and similar compositions of magnesium-bearing calcite via the PILP process further supports our hypothesis that the PILP process may play a fundamental role in the formation of calcitic biominerals in nature. In the realm of biomimetic engineering, the PILP process may also establish itself as a new method to produce thin ceramic films with variable compositions under ambient conditions. (c) 2007 Elsevier B.V. All rights reserved.