We describe unique crystal morphologies of hydrophobic CaCO3 crystals in a mixture of water and tetrahydrofuran (THF). After addition of sodium trisilanolate [(c-C5H9)(7)Si7O9(ONa)(3)] (1) into the mixture of water and THF, calcium reactants (0.1 M CaCl2 and 0.1 M (NH4)(2)CO3) were added to the reaction mixture at 30degreesC. FT-IR and SEM images showed that concave terraced calcite was obtained in 80% THF solution. In the absence of 1, the crystalline product was a mixture of rhombohedral calcite with aggregated vaterite particles. The hydrophobic modified surface of the concave terraced calcite was confirmed by the contact angle and dispersability in organic solvents. (C) 2003 Elsevier B.V. All rights reserved.