Coral-like porous morphologies with nanoscale cellular framework of CaCO3 crystals were produced through self-organized precipitation with silicate ions. Platy aragonite subunits in the porous structures were individually covered with silicate envelopes. Addition of seed crystals initiated preferential formation of the cellular aragonite. Spherical clusters of the cellular structures developed into coral-like morphologies with outgrowth of strange projections. (C) 2002 Elsevier Science B.V. All rights reserved.