Researchers discover a crystalline compound that opens the door to a new carbon chemistry
An international research team, led by scientists from the University of Valencia, has synthesised a "new crystalline compound": a calcium silicon double carbonate formed under conditions of pressure and temperature similar to those found in the Earth’s mantle. According to one of the principal investigators, David Santamaría , professor in the Department of Applied Physics and researcher at the UV’s Institute of Materials Science , the discovery "opens the door to a new carbon chemistry under extreme conditions".
The results of this Spanish-German collaboration have just been published in the international edition of the prestigious journal Angewandte Chemie. The article demonstrates the "importance of the finding", which "extends from materials science to geochemistry", Santamaría notes. He explains how carbonates form in the Earth’s crust from carbon dioxide (CO2) dissolved in water, which reacts and precipitates with metal cations. As tectonic plates move, these minerals penetrate into the mantle at subduction zones. This is a "key" process in the long-term regulation of terrestrial CO2, known as the "deep carbon cycle".
In areas close to subducting plates, carbonate and silicate minerals coexist. However, the existence of the reported crystalline phase, in which silicate and carbonate groups are structurally linked, "suggests that, under certain pressure and temperature conditions, more complex solids may form than traditional models assumed for silicate-carbonate interactions in the deep mantle", explains the University of Valencia researcher.
Implications and significance
The main implications of the discovery lie in "the potential existence of silicate-carbonate phases in deep underground formations and in improving our understanding and modelling of carbon storage mechanisms at geological scales", says Santamaría.
At the same time, experimental observation revealed that this crystalline phase is "metastable under ambient conditions". This is a finding of "major scientific relevance", as it shows how "kinetic barriers oppose and inhibit its free transformation into the energetically most favourable structure at room temperature and pressure, allowing the dense phase to be recoverable".
The most familiar example of metastability is diamond: "it forms under high-pressure and high-temperature conditions in the mantle, reaches the Earth’s surface through geological processes and persists because its transformation into graphite is kinetically inhibited", Santamaría explains.
The researchers conclude that this discovery paves the way for a new mineral chemistry, since the structural interweaving present in the new compound "connects two of the most abundant mineral families on Earth: silicates and carbonates". "This type of reactivity under extreme conditions, but with phases that are potentially recoverable at ambient conditions, significantly broadens the compositional and structural landscape of the phases that may play a role in the deep carbon cycle", he adds.
Methodology
According to the professor of Applied Physics at the UV, to achieve the experimental observation of the synthesis and characterisation "for the first time" of a calcium-silicon double carbonate (with formula Ca2Si(CO3)4), in which silicon structural units ([SiO6] with octahedral coordination) and carbonate groups ([CO3] trigonal planar) are structurally interconnected through oxygen atoms, the team employed "cutting-edge techniques", including diamond anvil cells and high-power lasers. "Structural determination was carried out in situ using synchrotron X-ray diffraction, Raman spectroscopy and first-principles calculations", he comments.
The compound exhibits an "unprecedented topology" within MO-SiO2-CO2 systems (M = divalent metal). According to the researcher, "a phase with these characteristics had not previously been identified, and the few known silicate-carbonate minerals contained isolated silicate and carbonate entities".
The research team, led by David Santamaría and Benedito Donizeti Botan-Neto (Institute of Materials Science, University of Valencia), also includes collaborators from the University of Oviedo , the University of Frankfurt (Goethe-Universität Frankfurt am Main) and the German research centre Deutsches Elektronen-Synchrotron (DESY).
Article reference: B otan-Neto, B.D.; Santamaría-Pérez, D., et al. "Experimental Observation of a Calcium Silicon Double Carbonate". Angewandte Chemie International Edition 2026, ISSN: 1433-7851, 1521-3773. https://doi.org/10.1002/anie.202524999
