The design of supramolecular templates to direct the synthesis of organized inorganic materials is illustrated for aragonite (CaCO3), which is metastable under ambient conditions but found in gall-stones, fish otoliths, etc. Spreading of the template 5-hexadecyloxyisophthalic acid at the air/water interface is shown to result in the specific nucleation of aragonite from supersaturated calcium bicarbonate solution without additives.