This paper deals with the influence of silicate species on the morphogenesis of BaCO3 (witherite), one of the main component of "silica/carbonate biomorphs". The size of barium carbonate crystals decreases progressively and significantly with the increasing amount of Na-metasilicate (Na-MTS) in the crystallization environment. When the Na-MTS amount in the aqueous mother solution is less than 500 ppm, single well-shaped micrometric BaCO3 crystals are obtained. Higher Na-MTS concentrations (4000-5000 ppm) produce polycrystalline structures built by pseudo-hexagonal nano-rods. X-ray powder diffraction (XRPD) diagrams show the decrease of crystal size with Na-MTS concentration and point out as well that silicate groups can be slightly absorbed into the barium carbonate lattice. The last part of the paper is devoted to the first finding, in laboratory, of aragonite polycrystalline structures belonging to the family of "silica/carbonate biomorphs". (C) 2009 Elsevier B.V. All rights reserved.