According to a new study published on Sunday, December 18th, 2016, in the journal Science, the scientific community is now able to explain how the world’s most valuable and biggest diamonds are formed. The researchers believe that the large gems like the Lesotho Promise or world-renowned Cullinan start off drowned in liquid metal deep inside our planet’s mantle.
Evan Smith with the Geological Institute of America and the lead author of the study came up with his theory after carefully analyzing the biggest diamonds’ offcuts. These pieces that the jewelers disregard hold valuable clues that led the research team to their conclusion.
Upon examining roughly 30 large stones, the researchers have discovered small metallic grains trapped inside each diamond. These grains are mostly composed of sulfur, hydrogen, methane, carbon, and a mixture of nickel and metallic iron. Based on these findings, the researchers were able to conclude that the diamonds formed in the Earth’s mantle. However, as opposed to other smaller pieces, the largest diamonds have formed under specific conditions, more accurately when saturated by liquid metal.
Furthermore, the metallic grains found in the offcuts may also provide the researchers with a better understanding of the oxygen levels present in different parts of the Earth’s mantle. Because of the fact that most diamonds form at a depth of approximately 93 to 125 miles beneath the surface, the scientists’ only way to better understand diamond formation and the wide range of other mysteries that our planet still has in store for us deep underground is by looking at the metallic traces found inside the gems.
“Small droplets of this metallic liquid could advance our understanding of Earth’s deep mantle largely inaccessible for scientific observation”, reads the study.
When it comes to the presence of oxygen in the Earth’s mantle, the scientists were able to conclude that the chemistry is more oxidized near the surface. One clue that led to this claim is the presence of carbon in gas form, namely carbon dioxide, found in magmas following a volcanic eruption. Ultimately, according to Mr. Smith, previous theories predicted that several parts of the Earth’s mantle benefits from limited oxygen and also contains small amounts of metallic iron about 155 miles beneath the surface.
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