Fine particles of CaCO3 with different morphologies, habits, and sizes were synthesized via the AOT/isooctane/water reverse microemulsion technique with the emphasis on the competing effects of operating variables, including R value (reactants molar ratio), temperature, and additives. Three different additives, i.e., potato starch, ethylenediamine, and diethylenetriamine, were chosen to study their interaction with the R value ranging between 1/2 and 4, or with the temperature ranging between 25 and 65 degrees C. In general, all the variables investigated in this study had a great influence on the crystal morphology of CaCO3 that lead to a specific habit; nevertheless, they had only a moderate effect on the particle size, which fell in the range between submicron and microns. Particles of three interesting habits, i.e., doughnut, hexagonal plate, and disk, were observed. The microstructure of the three shapes was revealed using a high-resolution microscope. (C) 2010 Elsevier Ltd. All rights reserved.