The precipitation of calcium carbonate polymorphs in vitro at 37 degrees C.

In order to determine some of the factors that affect the formation of the three polymorphs of calcium carbonate in gallstones, its precipitation from undisturbed solutions containing calcium chloride and sodium bicarbonate was studied. The variation in the amount of calcium carbonate formed with time was studied by weighing the precipitate, and the percentages of calcite, vaterite, and aragonite were determined by x-ray diffraction (XRD) analysis. The effects of additives and stirring were noted. Minor changes in conditions were sufficient to affect the formation of the polymorphs, and all three polymorphs could be found simultaneously in some solutions. It is suggested that no great differences in precipitating conditions need to be postulated to account for the presence of different polymorphs in gallstones. Aragonite seems to be formed slowly in undisturbed conditions.