A tiny diamond from Brazil has provided scientists with remarkable new evidence that water may travel much deeper into Earth’s interior than previously thought.
Hidden inside the small gemstone, researchers discovered a mineral that appears to survive the crushing pressures and intense heat of the lower mantle, suggesting it could help carry water hundreds of kilometers beneath the planet’s surface.
The study, published in Scientific Reports, was carried out by a team of Brazilian researchers using the advanced Sirius particle accelerator at the Brazilian Synchrotron Light Laboratory.
The diamond itself measures only about 3 millimeters across, but it contains microscopic mineral fragments that act like natural time capsules.
These tiny inclusions were trapped inside the diamond when it formed hundreds of millions of years ago, preserving a record of conditions deep within Earth where direct exploration is impossible.
The scientists focused on one particular mineral called goethite. This iron-rich mineral is common on Earth’s surface and is responsible for the brown color seen in many soils.
It also forms on the ocean floor when iron-rich rocks react with water. One important feature of goethite is that it contains water as part of its crystal structure.
Until recently, many researchers believed goethite could not survive the journey into Earth’s deep interior. As oceanic tectonic plates sink beneath continents in a process called subduction, temperatures rise rapidly. Scientists thought the mineral would quickly break down into other minerals while releasing its water at relatively shallow depths.
However, the new discovery suggests the story may be much more complex.
The diamond came from the Juína region of Brazil, an area famous for producing rare super-deep diamonds. Unlike most diamonds, which form about 150 kilometers below Earth’s surface, these unusual stones originate at depths greater than 300 kilometers. They are eventually carried upward by magma during volcanic eruptions.
Although many of these diamonds have little value as gemstones because they contain dark mineral inclusions, those imperfections are extremely valuable to geologists. They preserve tiny samples from deep inside Earth that would otherwise never reach the surface.
Using powerful X-ray imaging and spectroscopy at the Sirius research facility, the team carefully mapped around 100 mineral inclusions inside the diamond. One inclusion stood out because it appeared to contain iron hydroxide, something rarely expected inside Earth’s mantle.
Further analysis confirmed the presence of goethite along with the minerals hematite and magnetite. Finding these three minerals together inside a sealed inclusion surprised the researchers because they normally would not exist together under surface conditions.
The discovery matches recent laboratory experiments showing that goethite can survive enormous pressures of up to 57 gigapascals and temperatures approaching 1,800 degrees Celsius. These are conditions found between about 900 and 1,250 kilometers beneath Earth’s surface in the lower mantle.
The researchers believe goethite may survive if it is protected inside cooler sections of sinking oceanic plates. As the mineral gradually changes into other iron-rich minerals, it releases the water stored within its structure deep inside the mantle.
This hidden water could play an important role in Earth’s geology. Water lowers the melting point of rocks, allowing small amounts of magma to form. Over long periods, this magma may slowly rise and contribute to volcanic activity. Some scientists believe this process may even help create the volcanic rocks that eventually carry super-deep diamonds back to Earth’s surface.
The study also represents an important milestone for Brazilian science. It is the first investigation of a super-deep diamond carried out entirely by a Brazilian research team using Brazilian scientific facilities.
Beyond revealing the remarkable journey of a tiny diamond, the findings offer fresh insight into how water moves through Earth’s interior.
They suggest that the planet’s deep mantle may be more connected to the surface water cycle than scientists once believed, helping researchers better understand the long-term processes that shape our dynamic planet.
