Experimental observations of CaSiO₃-CaTiO₃ perovskites: implications for Ca-rich inclusions observed in sub-lithospheric diamonds

Calcium perovskite is a major component of deep mantle phase assemblages and has been frequently identified, in retrograde form, as polyphase mineral inclusions within sub-lithospheric diamonds. Here experimental observations of synthetic samples demonstrate various properties of calcium perovskite minerals which have relevance for the interpretation of diamond-hosted inclusions. Ambient pressure diffraction and spectroscopy confirm the linear dependence of crystallographic unit cell volume and Raman peak shifts across the entire CaSiO₃-CaTiO₃ binary join. These systematics will allow verification of perovskite structure and constraint of inclusion composition, without destructive analyses, in future studies. Additionally, high pressure observations confirm that calcium perovskite minerals ≳ 80 mol.% CaSiO₃ undergo spontaneous amorphization during decompression at room temperature, meaning they are unrecoverable. Finally, the presence of water appears to expand the calcium perovskite stability field to lower pressure conditions, implying at least some appreciable water-solubility in these minerals.