Most diamonds occur in the thickest parts of continental plates
The largest diamonds ever mined in the world, differ not only in size and splendour, but also a unique story of their origin.
All of them were born from the molten metal, dissolving an excessive amount of carbon deep in the bowels of the planet.
This conclusion was formulated in a new study published in Science.
Evan Smith from the Gemological Institute of America claims that “most of the diamonds formed at depths of 150 to 200 km. most diamonds occur in the thickest parts of continental plates, and it is easy to prove — about 98% of all mined diamonds were discovered in these areas.”
However, some of the stones, for example the famous Cullian (the largest of the diamonds weighing over 3000 carats) are too big and too different from the rest that led scientists to the idea of some other place of their formation. Compounding the problem is that the study of such rocks is practically impossible — how to request and study the most expensive stone on the planet, and even carry with him experiences?
Smith tried to systematically track the diamonds that were of the same type and quality to jewelry processing and cutting. All the matter in the geological inclusions, which are sometimes stored inside the stones, they give geologists clues about in which part of the mantle could have formed the stone. As a result, the geologist was able to organize information. According to him, diamonds like Kuliana is an amazing anomaly that did not appear in the rigid tectonic plates, but somewhere deeper in the convecting mantle, i.e. at depths from 360 to 750 km!
Moreover, Smith managed to figure out how they became so big. It turned out that all the matter in the fragments of iron and Nickel subjected to high temperatures and pressure. “Previously, it was only a theory, not confirmed experimentally. 20 years we have been developing this hypothesis, but we had no evidence. These diamonds are special, because thanks to them we know deep in the mantle actually is metal,” he says.
Diamonds grow in conjunction with liquid metal, incredibly well dissolving carbon. When the metal becomes saturated with carbon, a part of him begins to precipitate and solidify, over time building up the layers and turning into a big diamond. The source of this carbon, however, is still in question. Smith argues that this carbon originally came from the earth’s crust: it is about the collision of tectonic plates in which one plate goes underneath another part of it sinks into the mantle. Thus, portions of the ocean bottom once too can go underground and become a huge diamond.
And big diamonds and smaller stones appear relatively close to the surface only in one case: they push a volcanic eruption, and where the stones got up abundantly of all, be kimberlite pipes in them and find most of the modern diamonds.
Smith plans to continue his studies, but some data was irretrievably lost. While processing these stones, as Cullian, metal particles were rejected by the jeweler as scrap and removed from the body of the stone. However, in the future we can hope that such garbage will become valuable scientific samples that will help scientists find out more about the underground activity of the planet.
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