Russian scientists identify rare carbonate mineral deep within Earth

Researchers from the Vernadsky Institute of Geochemistry and Analytical Chemistry, working with international collaborators, have identified a rare phosphorus-bearing carbonate mineral – bradleyite – preserved as an inclusion inside a diamond formed deep in the Earth’s mantle.

This is the first time bradleyite has been found in such conditions, offering strong evidence that the deep mantle hosts unique phosphorus-rich carbonate fluids involved in transforming rocks and driving diamond formation. This is reported by the Ministry of Science and Higher Education of the Russian Federation.

Carbonate minerals such as calcite and dolomite typically form at low pressures in marine sediments and only occasionally appear in unusual alkaline magmatic rocks known as carbonatites. The newly identified bradleyite, with the chemical formula Na₃Mg(PO₄)(CO₃), formed hundreds of kilometres beneath the surface under extreme pressure and temperature before being transported upward by kimberlitic magma.

The study shows that bradleyite belongs to a deep-mantle carbonate association that also includes chlorine-, fluorine- and phosphorus-bearing phases. According to the authors, this highlights the far greater role of volatile and light elements in deep-Earth mineral formation than previously assumed, challenging long-held views that the mantle produces only silicates, oxides and ore minerals.

The team has also determined the crystal structure of bradleyite for the first time, using advanced analytical techniques including electron microscopy, diffraction methods and three-dimensional structural modelling. Scientists believe the discovery of this carbonate inclusion within a diamond provides new insights into how rare and light elements participate in deep-mantle processes.

Photo: Jacob Wackerhausen / iStock