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

¹ Astrophysics Group, Keele University, Keele, Staffordshire, ST5 5BG, UK
e-mail: s.j.day@keele.ac.uk
² Diamond Light Source, Harwell Science and Innovation Campus, Chilton, Didcot, Oxon OX11 0QX, UK

Received: 21 January 2013
Accepted: 13 March 2013

Abstract

Aims. 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.

Methods. 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.

Results. 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.

Conclusions. 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.