Calcium carbonate (CaCO3)/iron oxide composites were synthesized through a simple one-step impregnation procedure by mixing iron oxide nanoparticles (γ-Fe2O3 and Fe3O4) of about 6 nm in size and CaCO3 microparticles (Φ = 2 µm–8 µm, vaterite phase). The morphology and structural properties of CaCO3, iron oxide nanoparticles and CaCO3/iron oxide composites were characterized as a function of low iron content (0 %w to 3.2 %w) by scanning electron microscopy and transmission electron microscopy, X-ray diffraction and 57Fe Mössbauer spectrometry. The phase transformations induced by thermal treatment and laser irradiation were investigated in situ by X-ray thermodiffraction (XRTD) and Raman spectroscopy. We have shown that the phase transformations observed by XRTD are also observed under laser irradiation as a consequence of the absorption of the laser irradiation by iron oxide nanoparticles. Copyright © 2012 John Wiley & Sons, Ltd.