The mystery of two special South African diamonds has stunned the scientific community.

The rare composition of two South African diamonds not only intrigues but also reveals how diamonds are formed deep within the Earth.

A pair of diamonds formed hundreds of kilometers deep in the Earth's pliable mantle have been found to contain grains of materials that formed in completely opposite chemical environments. It's a combination so unusual that researchers think their coexistence is "almost impossible." The presence of these substances provides insight into the chemical processes of the mantle and the reactions that form diamonds. Image: Yael Kempe and Yakov Weiss.

The two diamonds were found in a mine in South Africa. Like many other gemstones, they contain what are called inclusions – tiny pieces of surrounding rock that were trapped when the diamond formed. Most jewelers hate these inclusions, but they provide interesting information for scientists . Photo: Shutterstock.

This is especially true when diamonds form deep in the inaccessible mantle, as they carry these inclusions to the surface virtually undisturbed – the only way such minerals can rise hundreds of kilometres without being altered from their original state in the deep mantle. Photo: Suzette Timmerman.

The two extraordinary new diamonds both contain inclusions of carbonate minerals rich in oxygen atoms (a state known as oxidized) and nickel alloys poor in oxygen (a state known as reduced, in chemistry terms). Just as acids and bases react immediately to form water and salt, oxidized carbonate minerals and reduced metals do not coexist for long. Photo: Suzette Timmerman.

Typically, diamond inclusions show only one of the two. So the presence of both in the diamond sample puzzled Yaakov Weiss, a senior lecturer in Earth sciences at the Hebrew University of Jerusalem, and his colleagues. Photo: Graham Pearson.

After closely analyzing the two diamonds, the researchers realized that the inclusions captured a “moment” of the reaction that created the sparkling stones, confirming for the first time that diamonds can form when carbonate minerals and reduced metals in the mantle react. This is the first time scientists have seen the midpoint of that reaction recorded in a natural diamond. Photo: TomekD76/iStock.

The discovery has important implications for what lies in the mysterious middle layer of the mantle. As we go deeper into the Earth, away from the surface, rocks and minerals become increasingly scarce, with fewer and fewer oxygen molecules, but there is little direct evidence of this shift in the mantle. Image: Graham Pearson.

Two new diamond specimens, found at depths of 280 to 470 kilometers below Earth's surface, provide the first real evidence of the theoretical chemical composition of the mantle. Weiss said the experts found oxidized molten material that existed deeper than expected. Kimberlite, the volcanic rock that brought diamonds to the surface, is so oxidized that researchers thought it couldn't form below 300 kilometers. Photo: Wenjia Fan, W. Design Studio.

However, this recent discovery suggests that oxidized rocks exist at deeper depths, and therefore kimberlites may as well. The diamond-forming reaction likely occurs when carbonate fluids are pulled down by subducting tectonic plates, bringing oxygen-rich minerals into contact with metal alloys in the mantle. Image: Gem Diamonds Ltd.

Nickel-rich inclusions may also help explain a strange phenomenon in some diamonds: nickel atoms sometimes appear to replace carbon in the crystal lattice of these diamonds. Photo: Shutterstock.

Readers are invited to watch the video : Witness the "treasure mountain" filled with gold and precious stones of Russia.

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