A double water-in-oil-in-water emulsion system was used as a biomimetic environment for the preparation of calcium carbonate particles. Calcium ions were extracted from an external aqueous phase (calcium nitrate solution) into the organic membrane phase (kerosene containing Span 83 as a surfactant and bis(2-ethylhexyl)phosphoric acid as an extractant) and stripped into the internal aqueous phase (sodium carbonate solution), where the precipitation of calcium carbonate occurred. In this pseudovesicular system it has been found that both the physical and polymorphic forms of the particles could be controlled by change of pH and method of demulsification such that either calcite or vaterite appeared as single crystals or heirarcically ordered aggregates.