Non-aqueous formation of the calcium carbonate polymorph vaterite: astrophysical implications

TL;DR

This study demonstrates the formation of the metastable mineral vaterite from calcium carbonate in simulated astrophysical conditions, suggesting its potential presence in space and planetary environments.

Contribution

It provides the first detailed structural analysis of vaterite formation via solid-gas interactions under astrophysical conditions.

Findings

Vaterite forms alongside calcite at elevated CO2 pressures.

Vaterite remains stable over a wide temperature and pressure range.

The formation process suggests vaterite could be part of extraterrestrial carbonate dust.

Abstract

We study the formation of calcium carbonate, through the solid-gas interaction of amorphous Ca-silicate with gaseous CO2, at elevated pressures, and link this to the possible presence of calcium carbonate in a number of circumstellar and planetary environments. We use in-situ synchrotron X-Ray powder diffraction to obtain detailed structural data pertaining to the formation of the crystalline calcium carbonate phase vaterite and its evolution with temperature. We found that the metastable calcium carbonate phase vaterite was formed alongside calcite, at elevated CO2 pressure, at room temperature and subsequently remained stable over a large range of temperature and pressure. We report the formation of the calcium carbonate mineral vaterite whilst attempting to simulate carbonate dust grain formation in astrophysical environments. This suggests that vaterite could be a mineral component of carbonate dust and also presents a possible method of formation for vaterite and its polymorphs on planetary surfaces.