Silicon carbonate, Si[CO<sub>3</sub>]<sub>2</sub>, is a potential carbon host in the deep Earth.
basic_science · Level V
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- Record sourced from PubMed, PMID 42213830.
- Also identified by DOI 10.1126/sciadv.aee5766.
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Abstract
The transport of carbon into the deep Earth is governed by the stability and properties of carbon-bearing phases. However, despite extensive research efforts, it is still an open question whether there are high-pressure minerals that can incorporate both silicon and carbon simultaneously. Multiple theoretical studies suggest that Si─C─O compounds could be stabilized at high pressures, but so far, no reliable experimental evidence for their presence has been presented. Here, we demonstrate that at 40(2) gigapascals and ≈ 1800(200) kelvin, CO<sub>2</sub> reacts with silicic acid or cristobalite and forms the anhydrous silicon carbonate Si[CO<sub>3</sub>]<sub>2</sub>. The structure consists of [SiO<sub>6</sub>] octahedra coordinated by six [CO<sub>3</sub>]<sup>2-</sup> groups. Similar groups occur in many ambient and high-pressure carbonates, suggesting that mixed carbonate-silicate phases may be stable at midmantle pressures. Silicon carbonate decomposes upon decompression at pressures of <6 gigapascals but could act as a potential host for carbon in Earth's lower mantle.