A groundbreaking study led by Yael Kempe and Yaakov Weiss at the Hebrew University’s Institute of Earth Sciences has uncovered the first natural evidence of nickel-rich metallic alloys in Earth’s mantle at depths of 280–470 km. Analysing diamonds from South Africa’s Voorspoed mine, researchers found rare nickel-iron metallic nanoinclusions and nickel-rich carbonates—uniquely preserved snapshots of deep mantle processes once only predicted by theory.
These diamonds act as tiny archives, trapping both reactants and products of a redox “freezing” reaction, where oxidised melts met reduced mantle rock. This interaction produces not just the diamonds themselves, but also volatile-rich magmas that later erupt to bring these gems to the surface.
What makes this discovery especially fascinating is its confirmation of decades-old predictions: that nickel-rich alloys should stabilise at specific mantle depths. Further, the mineral cargo inside these diamonds—such as solid nitrogen and high-pressure minerals—anchors their formation deep within the upper mantle.
Beyond theoretical validation, these findings offer a vivid picture of mantle chemistry in action. The co-existence of nickel-iron alloys and carbonates highlights how melt-rock interactions locally oxidise the mantle and drive dramatic geochemical changes. Such redox events shed new light on how diamonds form and how magmas that shape continents might originate.
Kempe and Weiss’s work not only marks the first natural confirmation of nickel-rich alloys at these depths, but it also demonstrates the extraordinary scientific value of inclusion-rich diamonds, often overlooked by jewellers. These “imperfect” stones are, in fact, nature’s deep-Earth storytellers—preserving volatile moments from hundreds of kilometres beneath our feet and revealing previously hidden processes that shape our dynamic planet.
The research paper titled “Redox state of the deep upper mantle recorded by nickel-rich diamond inclusions” is now available in Nature Geoscience and can be accessed at https://www.nature.com/articles/s41561-025-01791-4
Researchers:
Yael Kempe, Sergei Remennik, Oliver Tschauner, Oded Navon, Tim J. B. Holland and Yaakov Weiss
Institutions:
- The Freddy and Nadine Herrmann Institute of Earth Sciences, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
- The Harvey M. Krueger Family Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
- Department of Geoscience, University of Nevada, Las Vegas, NV 89154, USA
- Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, UK