The influence of ionic strength, magnesium ions and reactive surface area on calcite crystal growth morphology and surface microtopography /

The influence of ionic strength (I), magnesium ions and reactive surface area, on calcite crystal growth morphology and surface microtopography were investigated by transmission electron microscopy (TEM) and atomic force microscopy (AFM). Calcite overgrowths were precipitated from aqueous NaCl-NaHCO 3-CaCl2-MgCl2 solutions on reagent grade calcite seed powders and millimeter-size cleavage fragments in a chemo-stat system at 25ºC for up to 6 days. Aliquots of the reacting solutions were sampled regularly for analysis and the suspended seeds were separated for the preparation of Pt-C replicas and TEM imaging. Most cleavage fragments were recovered at the end of the experiments for AFM imaging.In all experiments, the euhedral {101¯4} rhombohedron of calcite seeds is modified at the same corners and edges within 24 hours of growth.In the parent solutions seeded with a smaller amount of calcite seed powders and at I = 0.13 m, the crystal morphology of calcite seed overgrowths consists of {101¯4} and a new, prismatic form. The use of a smaller amount of seeds translates into considerably higher precipitation rates per unit surface area and leads to the development of fewer, new morphological growth features