Calcite Formation from Nanoporous Amorphous Silicates in Interaction with Carbon Dioxyde

Introduction: Carbonates have been recently detected in dust shells of evolved stars [1] and protostars [2,3] suggesting that they could form under dry conditions (without liquid water). Around young stars, silicates are mainly magnesium-rich, amorphous and porous dusts [4], believed to form in the interstellar medium (ISM) by irradiation [5]. Such material is far from equilibrium and potentially highly reactive. In addition, their small size and their porosity should enhance their reactivity. More specifically, such material should undergo extensive transformations during gas-grain interaction that occurred in the nebula. Here we study experimentally the direct formation of carbonates from an amorphous and nanoporous Mg-Ca-rich silicate exposed to carbon dioxide rich atmosphere.