Carbonado black diamonds may originate from ancient asteroid impacts

A new study published in Gondwana Research offers a potential explanation for the mysterious origin of carbonados, also known as black diamonds. These porous, dark stones are found exclusively in riverbeds in Brazil and Central Africa, yet the source rock from which they originate has never been located.

Researchers led by Attila Demény and Péter Németh analyzed samples from the Brazilian Tombador formation, examining their chemical composition, structure, and carbon isotopes. Their findings suggest that an ancient, massive asteroid impact may have driven carbon-rich material deep into the Earth's mantle. Under extreme pressure, this carbon could have formed diamonds. If the material was pushed down quickly through subduction, the characteristic cavities of the carbonado might have been preserved.

Later, magma moving toward the surface could have brought these diamond-bearing rocks upward, where erosion eventually released them into river sediments. The study also addressed the stones' glassy surfaces, noting that they likely formed after the diamonds were created, possibly through mineral deposition and fluid interaction, rather than being a direct result of an impact shock.