Influence of silicate anions on the morphology of calcite crystals

Abstract

Calcite crystals with interesting morphologies were synthesized using various oligomers of silicate in solution. The crystals were grown by adding an appropriate amount of sodium silicate to a supersaturated calcium bicarbonate solution at room temperature. The morphology of nucleated calcite crystals changed significantly with the concentrations of silicate anion in solution. At lower levels, trapezoidal shaped crystals exhibiting indented and terraced structures were formed. At a Ca2+/silicate ion ratio of 1:1, oriented crystals with pseudohexagonal shapes were nucleated in solution. A higher concentration of sodium silicate produced polycrystalline calcite crystal aggregates. Powder XRD data indicates significant expansion of the calcite lattice because of the incorporation of silicate anions. We hypothesize that the observed sequential changes in morphology of calcite crystals with added silicate anion concentration may be due to the incorporation of monomeric, oligomeric, and polymeric forms of silicate anion species into the calcite lattice.