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Where are the rarest diamonds on Earth formed?

2022-10-25 20:07:12Lifestyle SHKRUAR NGA REDAKSIA VOX
Where are the rarest diamonds on Earth formed?
Where are the rarest diamonds on Earth formed?

In "pockets" of liquid metal, hundreds of kilometers deep in the Earth: the analysis of these stones with certain chemical structures reveals new information about the depth of the planet.

Not all diamonds are the same; for some such supergiants, reaching the value of 3000 carats and up to 10 cm in size, the origin has long been questioned. A study published by the journal 'Science' suggests that supergiant diamonds come from 'pools' of liquid metal, found several hundred kilometers deep within the planet.

Ordinary diamonds form with the Earth's mantle and come to the surface due to volcanic eruptions. But the most precious specimens, such as the Cullinan diamond or the "Star of Africa" ​​(the largest diamond ever found, weighing 621 grams, before it was broken into several pieces), or the Lesotho Promise, the 15th largest ever found, have an apparent structure and chemical composition quite different from the others, and little is known about how they formed.

Researchers from the Gemological Institute of America, in New York, the Carnegie Institution for Science, in Washington and the Department of Geosciences in Padua, have analyzed the crystal structures of 9 types of type II diamonds, the rarest on our planet.

They found within them mineralogical compounds made up of iron-nickel alloys, sulphites and iron carbide, a combination that had never before been observed in "normal" diamonds.

These compounds are also surrounded by a layer of methane and hydrogen, another very unusual feature. Analysis of another 42 type II diamonds revealed that the unusual alloy is present in 72% of the samples.

These chemical "signatures" have allowed researchers to identify the initial conditions and depth at which these diamonds formed.

The presence in them of a mineral called 'majorite' suggests an origin at depths of up to 750 km (at greater depths, majorite becomes unstable).

The crystallized metallic composition suggests that these types of diamonds formed in isolated 'pockets' of liquid metal deep within the Earth, separated from the oxygen-rich rocks where ordinary diamonds form. It is thought that these small reserves of liquid metal may make up about 1 percent of the Earth's mantle.

"The study opens a new scenario on geological processes in the depths of our planet," says Fabrizio Nestola, one of the authors of the study. – It shows how liquid iron can form in a region far from the earth's core; if the outer core, which is assumed to be composed of molten iron-nickel, starts at depths of 2900 km, the presence of mineralogical mixtures consisting of iron-nickel alloys, sulphites and iron carbides in these diamonds shows how they can be formed at a depth no greater than 1000 km".

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