Two of the world’s most famous diamonds may have originated deep below the earth’s surface, near the planet’s core.
All natural diamonds on Earth are first formed underground from our surface perspective. But from the perspective of this planet’s great mass, its usual births occur relatively far from the nucleus. Peel the earth like a lemon, and you would discover diamonds that grow at the bottom of the tectonic plates. Those diamonds form about 90 to 125 miles (150 to 200 kilometers) deep, under pressure that exists right where the crust meets the most fluid outer mantle, or the planet’s middle layer. There are no mines that go that far underground, but some of those diamonds go as far as humans can reach them.
The “Hope” diamond, a large and famous stone, as well as the “Cullinan” diamond, the largest rough gemstone ever found, are different. They are “super deep” stones, confirms new research. A 2018 article showed that these boron blue gemstones likely originated somewhere in the planet’s hot “mantle”, a region between the planet’s crust and liquid outer core, Live Science previously reported. This new research shows that, at least sometimes, deep stones form in this hot zone.
Related: 13 mysterious and cursed gemstones
Research presented today (June 24) at the Goldschmidt geochemistry conference, finds traces of a mineral called bridgmanite in two less famous diamonds of the same type as the famous gemstones.
All diamonds are carbon crystals and various chemical impurities. The type of any specific diamond is determined by impurities and other conditions present during its creation. Therefore, two diamonds of the same type probably formed under similar conditions.
Bridgmanite is a very common mineral within Earth, but it does not form in the crust or even in the upper mantle.
“What we really see in diamonds when they reach [the] “The surface is not bridgmanite, but the minerals remain when it decomposes as pressure decreases,” said Evan Smith of the Gemological Institute of America in a statement. “Finding these minerals trapped in a diamond means that the diamond itself must have crystallized at a depth where bridgmanite exists, deep within the Earth.”
This discovery, the researchers said, suggests that both large blue stones originated in the lower mantle, a fluid area that stretches from 410 miles (660 km) deep to the planet’s liquid outer core.
The first, a 20-carat “type IIb blue diamond” from South Africa, showed evidence of bridgmanite under examination with laser light. The 45.52-carat Hope diamond is a larger example of the same type of diamond.
Another diamond, a 124-carat stone the size of a walnut, is called a “CLIPPIR” diamond (meaning Cullinan, large, poor in inclusion, pure, irregular, and reabsorbed). He is from Lesotho, a country surrounded by South Africa. And, as its type suggests, it’s like the 3,106.75-carat Cullinan. The researchers already knew that CLIPPIRs came from far below the cortex, but this study offers the first direct evidence that they come from the lower mantle.
Neither Cullinan’s hope nor diamonds were studied as part of this investigation. But the researchers said that what is true for less famous stones is also true for more famous stones.
The Cullinan diamond no longer exists in its great original condition, as it has long since been cut into smaller stones for sale. The two largest are now part of Queen Elizabeth II’s “crown jewels”.
The massive rough diamond appeared in 1905 just 18 feet (5.5 meters) below the surface at the British-owned Premier mine in South Africa, a far cry from its birthplace in the lower mantle. He was quickly dispatched out of the region as part of the British imperial project that exploited and abused black workers to extract mineral wealth from the region, according to Rapaport, an international corporate network serving the jewelry market.
The precise origins of the Hope diamond are much more dangerous, but according to the Smithsonian Institution (which now has custody of the diamond), Kollur mine workers in India probably discovered the stone before it was sold to French merchant Jean Baptiste Tavernier. in 1668.
Karin Hofmeester, a historian at the International Institute for Social History in Amsterdam, wrote in an essay that men, women and children worked for thousands of people in these dangerous mines at the time in exchange for reduced wages and food. It is unclear who was responsible for the discovery of the Hope diamond or where exactly it appeared.
The researchers do know that when it was found it weighed 122.2 carats, according to the Smithsonian. Once cut to its current state, the Hope passed into the hands of the French royal family, wealthy British collectors, and then American businessmen before ending up in the Smithsonian, a world far removed from both the point of origin of the lower mantle and the mine in India. where was discovered
Originally published in Living science.