Growth of calcite crystals with non-singular faces

Abstract

Calcite crystals with non-singular faces were grown by the silica gel technique using the double diffusion of CaCl 2 (1N) and K 2C 2O 4 (1N) in silica gel, adjusted to pH 8. The experiments were conducted at 25°C and with an atmospheric pressure of CO 2. Calcite formation occurs under very low concentration gradients. The material was identified by X-ray diffraction and infrared spectroscopy techniques. The crystal morphologies were observed by ordinary microscopy and SEM. The synthesized calcite crystals show an unusual curved morphology with some flat faces that correspond to {10 1 1}. Curved surfaces can be ascribed to the region of {10 1 0} and {11 2 3}. The only observed impurity present in the crystals is 0.7% Si, which is equal to or even lower th an that found in calcite crystals with flat faces grown in gels under higher concentration gradients. Consequently the presence of Si as impurity is a dubious factor for the formation of such curved surfaces. The explanation must be a consequence of the kinetics of the growth process.