Crystal structure evolution of CaSiO3 polymorphs at Earth’s mantle pressure

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Marco E. Ciriotti
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Iscritto il: ven 25 giu, 2004 11:31
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Crystal structure evolution of CaSiO3 polymorphs at Earth’s mantle pressure

Messaggio da Marco E. Ciriotti » dom 20 giu, 2021 12:45

Referenza:
▪ Milani, S., Comboni, D., Lotti, P., Fumagalli, P., Ziberna, L., Maurice , J., Hanfland, M., Merlini, M. (2021): Crystal Structure Evolution of CaSiO3 Polymorphs at Earth’s Mantle Pressure. Minerals, 11, 652.

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 of the 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 tetrahedrallystructured 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.
Marco E. Ciriotti

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