Morphological development in calcium carbonate precipitation by the ethanolamine process at 30 and 60 degrees C has been examined using different techniques (quantitative image analysis, laser diffraction, XRD, and FT-IR). The initially grown phase is of vaterite modification that at higher temperatures (60 degrees C) transforms to a more stable aragonite phase within the reactor itself. A comparison of the form and structure of calcium carbonate particles obtained during the process leads to a conclusion that crystal aggregation is the mechanism that determines the overall particle size at lower temperatures (30 degrees C), while crystal growth dominates at higher temperatures. The results show that crystal characterization by quantitative image analysis permits a better understanding of the phenomena taking place in the reactor.