Calcium silicate-diorthocarbonate is a missing link in deep-mantle chemistry of silicates and carbonates.

High-pressure calcium silicate-diorthocarbonate (CaSiC2O7) was synthesized at 122 GPa, revealing a new phase that links silicates and carbonates in deep-mantle chemistry.

• Why it matters: Understanding interactions between silicates and carbonates is crucial for interpreting planetary processes and seismic data, yet high-pressure compounds bridging these groups have been elusive.
• What they did: Researchers used experimental synthesis at extreme conditions combined with ab initio calculations to produce and verify the stability of CaSiC2O7, a structure based on vertex-sharing SiO6 octahedra and CO4 tetrahedra.
• The result: The discovery suggests a new pathway for carbonate-silicate interactions in the deep mantle, with CaSiC2O7’s low density and acoustic velocities potentially explaining seismic anomalies near the core-mantle boundary.