Calcium carbonate (CaCO3) was crystallized in xanthan (XC) aqueous solutions. The CaCO3 particles were characterized by scanning electron microscopy (SEM), powder X-ray diffraction (XRD), Fourier transform infrared (FIR) spectroscopy and thermogravimetry analysis (TGA) methods. The concentrations of XC, Ca2+ and CO32- ions and the ratios [Ca2+]/[CO32-] and [Mg2+]/[Ca2+] show evident influence on the aggregation and growth of CaCO3 particles. The presence of Mg2+ ions influences not only the morphology, but also the polymorph of CaCO3. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.