Confinement generates single-crystal aragonite rods at room temperature.

Area of Science:

• Geochemistry
• Biomineralization
• Materials Science

Background:

• Calcite and aragonite polymorphism is crucial in biomineralization and paleogeochemistry.
• Organisms selectively produce aragonite and calcite, but the mechanisms remain unclear.
• Previous research focused on organic macromolecules, overlooking environmental factors.

Purpose of the Study:

• To investigate the role of confinement in calcium carbonate polymorph formation.
• To explore if pore size influences the selective precipitation of calcite and aragonite.

Main Methods:

• Precipitating calcium carbonate within track-etched membranes with controlled pore sizes.
• Systematically analyzing polymorph formation as a function of membrane pore diameter.

Main Results:

• Aragonite formation increased as pore size decreased.
• 25-nm pores exclusively produced oriented single crystals of aragonite.
• Significant aragonite was observed in 200-nm pores with low Mg/SO4 concentrations.

Conclusions:

• Confinement effects, particularly pore size, significantly influence calcium carbonate polymorph selection.
• Organisms may leverage confinement to control calcite and aragonite formation.
• Pore size impacts ion distribution, becoming critical in nanoscale environments.