Very rare blue diamonds lurk deep in the Earth’s core



Blue diamonds form hundreds of kilometres below the earth’s surface

Scientists have discovered that it is very rare and expensive blue diamonds are formed hundreds of kilometers beneath the surface of the earth.

The rarest diamonds on Earth were forged, hundreds of kilometres below the surface, scientists announced on Thursday.

A team of geologists and gemologists from Australia and the US analysed 46 blue diamonds, including one from South Africa that sold for $25 million in 2016, to determine that the precious gems are formed at a depth of 410 km under the earth’s surface. The findings were published in the journal Nature.

For perspective, the International Space Station orbits about 250 miles above the Earth, and the deepest humans have ever drilled below the surface, is about seven miles.

Blue diamonds consist of approximately 0.02 percent of the mined diamonds, according to the experts, but also some of the world’s most beautiful jewels. Their origins long shrouded in mystery.

“We knew essentially nothing about where they grow,” geologist Evan Smith, lead author of the report and a researcher at the Gemological Institute of America in New York, told the Washington Post.

The color of these rare gems tipped scientists how they were formed. Their striking blue hue, which is partly dependent on the amount of the element boron in the gem captures is helping scientists to unlock the mysteries deep in the earth’s core.

A blue, boron-bearing diamonds is examined as part of the study announced in Nature.

(Evan Smith/Gemological Institute of America)

“We have always known there is something special about these diamonds,” geologist Jeffrey Post, curator of the mineral collection of the Smithsonian’s National Museum of Natural History, who was not involved in the Nature report, said in the newspaper. Post added that the authors make a “very convincing argument” that these diamonds formed larger than that of the average depth.


The researchers concluded that the boron-colors of the diamonds is the same as the drill found in the ocean floor. However, that spurred more questions.

As the seafloor ages and becomes colder, it eventually becomes denser than the mantle below it and sinks. The drill, which is covered by a protective rock, heads km underground to the lower mantle.

That deep, hidden area of extreme heat and pressure is where the rare blue diamond to be formed. And they still have to make a trip millions of years back in the direction of the surface.

“It gives us an idea of how the layers of the Earth, recycling, Megan Duncan, an Earth scientist at the University of California, Davis, who was not involved in the study, told Scientific American.

Christopher Carbone is a reporter and news editor covering science and technology for He can be reached at Follow him on Twitter @christocarbone.

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