Do stable prenucleation clusters exist in calcium carbonate solutions
In plain words
Experiments reported small, stable ion clusters in calcium carbonate solutions even before the solution is saturated, which classical theory forbids. Whether these clusters are truly stable or are short-lived precursors of a dense liquid phase is disputed.
Precise statement
Clusters of about $20\ \mathrm{Angstrom}$ were reported in 2008 in undersaturated and supersaturated CaCO3 solutions, with properties inconsistent with CNT. Determine whether they are thermodynamically stable solute species (negative formation free energy over a range of concentrations) or kinetically persistent ion associates or droplets of a dense liquid formed by liquid-liquid separation, from measured cluster size distributions and formation free energies versus concentration and pH.
What would settle it
Quantitative measurement of the cluster size distribution and its concentration dependence, compared with free-energy calculations, showing stable solutes or metastable dense-liquid droplets.