Researchers at the Max Planck Institute in Golm near Potsdam have now made a contribution to achieving this aim by demonstrating that calcium carbonate crystals are created differently from the way they were previously thought to form. When calcium and carbonate ions come together in a solution, they form stable nanoclusters consisting of around 70 calcium and carbonate ions - and they do that even in very soft water, a dilute solution from which chalk does not normally precipitate. If the concentration of dissolved calcium carbonate is increased, the clusters clump together and the mineral crystallizes.
Order at an early stage
"It seems that it is already decided when the clusters form, which of the three anhydrous crystal structures calcium carbonate will assume," says Helmut Clfen who headed the study. "We also observed that the crystal structure depends on the pH level." The pH level indicates the acidity or alkalinity of a solution. Under low alkaline conditions, calcium carbonate forms calcite, its most stable crystalline structure. In a more alkaline environment, it creates vaterite, a non-stable crystalline structure.
"Our results suggest that the pH level influences the way the ions group together in these clusters, which are just two nanometers in size," explains Denis Gebauer, who played a crucial part in the study. At this stage, they do not form a regular crystal structure, but it is highly likely that the rudimentary arrangement of the crystal is already recognizable. If the clusters then group together into increasingly larger aggregates, this arrangement can remain in place. A transient amorphous form, that is, a non-crystalline solid, is initially created, which then changes into a crystal.
Easier for organisms to intervene
If crystallization really did take this route, it would be easier to understand how mussels, for example, construct their shells or a sea
|Contact: Dr. Helmut Coelfen|