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This surprising discovery has never appeared in nature before and reveals secrets about the mantle

Diamonds formed deep in the mantle contain a mineral that has never been seen in nature. This discovery is a rare glimpse into the depths of the mantle and may help reveal new information about the structure of the Earth at a depth of more than 660 kilometers. In turn, this can help geologists better understand how the mantle controls the tectonic plates of the earth.

The mineral perovskite silicate perovskite is only formed under incredible high pressures that occur deep in the earth. Oliver Tschauner, a mineralogist at the University of Nevada in Las Vegas, said the newly discovered samples may have formed 660 to 900 kilometers below the earth's surface. Although this mineral was previously synthesized in a laboratory using a pressure of 20 gigapascals (almost 200,000 times the atmospheric pressure), when it was taken out of an artificial high-pressure environment, it immediately returned to another form. Therefore, researchers believe that it is impossible to extract natural perovskite silicate perovskite from the mantle. Tschauner said: "We believe that the probability of finding it is so low that we have never really actively searched for it."

Therefore, when he and his colleagues analyzed the defects of the diamond from Olapa, Botswana, they found three tiny spots of perovskite perovskite, which surprised him. Calcium silicate exists in other forms, including wollastonite in the earth's crust and braestone in the middle and lower parts of the mantle. But this version has an obvious cubic crystal structure, which marks that it is different from those of the mineral version. Tschauner and his colleagues named this new mineral "davemaoite", named after geologist Ho-Kwang "Dave" Mao. He conducted some groundbreaking experiments, using diamonds as a press, through experiments on the earth The surface produces pressure similar to that of the mantle. They announced the discovery in the journal Science on Thursday.

Geoscientists can understand the composition of the mantle based on what is present in the earth's crust, because the mantle and the rocks in the crust are connected: structures move rocks and minerals up and down between layers over millions of years. However, minerals deform and change as they leave the high pressure and hot temperature of the lower mantle. Diamonds are the only direct window into the area because they will not deform. They are formed at least 150 kilometers below the surface, and some originate at a depth of 1,000 kilometers. The crystal structure of diamonds is made of pure carbon, but they often absorb the tiny fragments around them when they are formed. Because diamonds are very hard, they can seal these tiny "inclusions" under very high pressure-even if the diamonds rise to the crust and are picked by miners. "Diamonds don't let anything in or out," said Oded Navon, a geologist who studies diamonds and deep mantle at the Hebrew University of Jerusalem, but was not involved in the identification of davymau. "It really is a perfect closed box."

The amount of davymau in Botswana diamonds is extremely small, and each of the three spots is only about 5 to 10 microns wide. Tschauner and his colleagues used X-rays to analyze the contents, then used a laser to drill into two of them, evaporate the material and send it to a device called a mass spectrometer to determine the elements that make up the sample. They found that the potassium content of Davymite is surprisingly high. Tschauner said this may help stabilize the stability of mantle minerals during their stay on the earth's surface. Fei Yingwei, a geochemist at the Carnegie Institute of Science, said that high potassium levels also imply that a global "conveyor belt" circulates elements between the crust and the deep mantle. Under study. Potassium is not the main element in the deep mantle, but it may move in the crust of the subduction zone, where one tectonic plate is pushed under another.

Tschauner said that one form of potassium is radioactive, and Davimorite also contains small amounts of radioactive elements, such as thorium and uranium, which are not easily absorbed by other minerals that make up the lower mantle. Tschauner said this is important because the decay of these elements generates about one-third of the heat in the Earth's interior. Extrapolating from mineral concentrations closer to the surface of the earth, geoscientists suspect that Davymauite accounts for about 5% to 7% of the lower mantle. But this mineral may be unevenly distributed, Tschauner adds. Because of this, Davemaoite, which is rich in uranium and thorium, may dominate in some places-which may explain why some parts of the mantle are hotter than others. These hotspots help promote circulation in the mantle and thus promote plate tectonics, so small changes in mineral concentration may have a huge impact on the surface of our planet. This change may also reveal more connections between the crust and its lower mantle, and may help explain how elements move between them. Tschauner said this is a field of research that is just becoming possible. "Allowing real minerals from the lower mantle to still exist is a fairly new direction for this type of research," he added.

Stephanie Pappas is a freelance science journalist. She lives in Denver, Colorado.

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