Crystal Structure Evolution of CaSiO3 Polymorphs at Earth’s Mantle Pressures

Abstract

CaSiO3 polymorphs are abundant in only unique geological settings on the Earth’s surface and are the major Ca-bearing phases at deep mantle condition. An accurate and comprehensive study of their density and structural evolution with pressure and temperature is still lacking. Therefore, in this study we report the elastic behavior and structural evolution of wollastonite and CaSiO3-walstromite with pressure. Both minerals are characterized by first order phase transitions to denser structures. The deformations that lead to these transformations allow a volume increase ofthe bigger polyhedra, which might ease cation substitution in the structural sites of these phases. Furthermore, their geometrical features are clear analogies with those predicted and observed for tetrahedrally-structured ultra-high-pressure carbonates, which are unfortunately unquenchable. Indeed, wollastonite and CaSiO3-walstromite have a close resemblance to ultra-high-pressure chain- and ring-carbonates. This suggests a rich polymorphism also for tetrahedral carbonates, which might increase the compositional range of these phases, including continuous solid solutions involving cations with different size (Ca vs. Mg in particular) and important minor or trace elements incorporation.

Investigation of Porous Ceramic Structures Based on Hydroxyapatite and Wollastonite with Potential Applications in the Field of Tissue Engineering

“…Wollastonite is found in two polymorphic forms: β-wollastonite, corresponding to low temperatures, and above 1124 • C, which passes into the α-wollastonite phase, formed at temperatures up to 1454 • C [7,8]. In the medical field, the β polymorphic form is preferred for use, due to the phase arrangement of its two constituent components, which leads to an increase in the mechanical and chemical properties of the material [9,10].…”