Superdeep diamond studied at CNPEM reveals mineral that transports water into the center of the Earth

Research led by scientists at Sirius found these diamonds contain a hydrated compound that can reach thousands of kilometers deep

Researchers from the Brazilian Center for Research in Energy and Materials (CNPEM) and other national collaborators have discovered unprecedented proof that water can be transported to regions deep within the Earth. The study, published in Scientific Reports (a journal in the Nature group), analyzed a rare diamond from Juína, Mato Grosso, and identified a complex mineral capable of carrying water to the lower mantle, offering new clues about how the planet stores and circulates water hundreds of kilometers below its surface. 

The diamond is considered “superdeep,” formed under extreme conditions up to 800 kilometers below the Earth’s crust. This type of diamond is found in only a few places in the world; Juína is the main area where they are known to occur. Without significant commercial value as gemstones, these diamonds are generally used to produce cutting and grinding instruments, as well as surgical and precision tools. The CNPEM researchers initially obtained samples of these stones as donations from small-scale miners in the region, and later acquired new diamonds with funding from the Serrapilheira Institute. 

The team found an inclusion of ferrous oxyhydroxide inside the diamond, composed of a combination of minerals such as goethite, hematite and magnetite. This combination forms a hydrated material that could serve as a “vehicle” capable of transporting water from the Earth’s surface to extremely deep regions. 

The discovery is notable because the area deep within the Earth is subject to extreme temperatures and pressures. Temperatures can exceed 2,000 °C in regions of the mantle, an environment in which hydrated minerals capable of storing water or hydroxyl groups in their crystalline structure tend to become unstable.  

“When we talk about the inside of the planet, we don’t think of hydrated minerals at such extreme depths. For this reason, any mineral that can maintain hydroxyls trapped within its crystalline structure under these conditions is extremely important for understanding how water can exist and circulate in the lower mantle,” explained Fernanda Gervasoni, a professor and researcher at the Federal University of Pelotas and CNPEM collaborator. 

The research involved advanced synchrotron light techniques at Sirius, CNPEM’s fourth-generation particle accelerator, using the Mogno, Ema and Carnaúba beamlines. The state-of-the-art infrastructure made it possible to observe the composition and structure of the mineral preserved in the diamond at extremely high resolutions. 

According to Gervasoni, the mineral they found probably originated from subduction zones, regions where the tectonic plates plunge inside the Earth, and underwent transformations under very high pressures and temperatures. During the process, the material would have released water and oxygen into the lower mantle. 

“Water at these depths does not mean that underground oceans exist, but rather hydroxyls incorporated into the crystalline structure of minerals. Still, this profoundly alters the dynamics of the planet’s interior, and can influence processes such as rock fusion, magma formation and even the occurrence of deep earthquakes,” she added, explaining that the mineral was generally ignored in the past in similar studies. “When it appears in diamonds, this mineral is often treated as surface contamination. But we demonstrated that this inclusion was completely isolated inside the stone, without contact with fractures or with the external environment.” 

This scientific finding reinforces the hypothesis that the water cycle on Earth is much more complex than previously imagined, involving not only oceans and the atmosphere but also processes deep inside the planet. Additionally, the release of water and oxygen at great depths can alter the fundamental properties of the mantle, such as its chemical composition, dynamics and physical behavior, affecting large-scale geological phenomena. 

“The most interesting thing is that we observe the transformation of this mineral taking place within the inclusion, indicating that it had probably already released water inside the Earth. This helps us to better understand the chemical and physical processes that occur in extremely deep regions of the planet,” said Gervasoni. 

The study brings together a group of scientists from CNPEM, as well as researchers from the University of Brasilia (DF), the Federal University of Pelotas (RS) and the Federal University of Rio Grande do Sul (RS). The research also received funding from FAPESP, which supports Fernanda Gervasoni’s post-doctoral research.