The diamonds were discovered at the De Beers Group’s Voorspoed Mine in South Africa and studied by experts at Hebrew University's Institute of Earth Sciences and Nanocenter in Israel.
One diamond contains nickel-rich carbonate minerals formed in an oxidised, oxygen-rich environment. The other contains nickel-iron alloys linked to a reduced, oxygen-poor environment. These materials typically react and neutralise each other, making such a pairing unlikely.
“The find has implications for what lies in the mantle’s mysterious middle. As you travel deeper into the earth, away from the surface, the rocks and minerals become increasingly reduced, with fewer and fewer oxygen molecules available, but there is little direct evidence of this shift from the mantle,” writes Stephanie Pappas for Scientific American.
“Theoretical calculations have given researchers a notion of how the planet shifts from oxidised to reduced with depth.”
Pappas added: “These new samples, which come from between 280 and 470 km below Earth’s surface, provide the first real-world fact-check on this theoretical mantle chemistry.”
Researchers Yael Kempe and Yaakov Weiss suggest that a process known as “redox freezing,” which occurs when changing conditions suddenly halt chemical reactions, may explain their coexistence. A rapid change in temperature or pressure deep underground may have stopped the expected reaction. This allowed both diamonds to retain their distinct compositions.
The findings, which have been published in Nature Geoscience, provide new evidence about diamond formation more than 150 kilometres below the Earth’s surface.
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