Calcium carbonate was synthesized according to a generic three-phase synthesis route in the presence of self-assembling liquid crystalline phases, and a comparison was made between the products formed in hexagonal and reverse hexagonal liquid crystalline phases. The surfactants used to form the liquid crystalline phases were the three different triblock copolymers Pluronic P105 (hexagonal) and P104 or P123 (reverse hexagonal), consisting of poly (propylene glycol) as the middle block and poly (ethylene glycol) as the end blocks. An aqueous solution of CaCl2 was mixed with the Pluronics and organic solvents to make up the liquid crystalline phases, which subsequently were exposed to CO2 (g), resulting in the formation of CaCO3. The specific surface areas of the CaCO3 products obtained varied front 5 to 226 m(2)/ g, depending on the initial concentration of CaCl2. Small-angle X-ray scattering showed that the reactant salt and the CaCO3 crystals were situated in the water domains of the liquid crystalline phases and that these remained throughout the course of the experiment. Transmission electron microscopy studies in combination with powder X-ray diffraction revealed that CaCO3 with high specific surface areas consisted of fibrils with the vaterite structure and formed at low CaCl2 concentrations. Samples of lower surface areas consisted of flakes with the calcite structure and formed predominantly at higher CaCl2 concentrations. Nitrogen adsorption showed a narrow pore size distribution for some of the materials prepared in the reverse hexagonal phases. Poly(acrylic acid) added to a hexagonal phase increased the specific surface area of the CaCO3 substantially, whereas when added to a reverse hexagonal phase no increase in surface area was found. Powder X-ray diffraction showed that higher specific surface areas obtained with poly(acrylic acid) were associated with the formation of a larger fraction of amorphous CaCO3.