Stable Prenucleation Calcium Carbonate Clusters

TLDR

Calcium carbonate forms scales, geological deposits, biominerals, and ocean sediments, yet its precipitation mechanism remains poorly understood, challenging classical nucleation theories that assume metastable ion clusters. The authors characterize prenucleation cluster formation using equilibrium thermodynamics and a multiple‑binding model that captures structural preformation. They demonstrate that stable prenucleation ion clusters exist even in undersaturated solutions and are the key species driving calcium carbonate nucleation, implying similar mechanisms may govern other mineral crystallizations.

Abstract

Calcium carbonate forms scales, geological deposits, biominerals, and ocean sediments. Huge amounts of carbon dioxide are retained as carbonate ions, and calcium ions represent a major contribution to water hardness. Despite its relevance, little is known about the precipitation mechanism of calcium carbonate, and specified complex crystal structures challenge the classical view on nucleation considering the formation of metastable ion clusters. We demonstrate that dissolved calcium carbonate in fact contains stable prenucleation ion clusters forming even in undersaturated solution. The cluster formation can be characterized by means of equilibrium thermodynamics, applying a multiple-binding model, which allows for structural preformation. Stable clusters are the relevant species in calcium carbonate nucleation. Such mechanisms may also be important for the crystallization of other minerals.