Friday, December 3, 2021

Mineral composition of Botswana’s diamond puzzles geologists

All eyes are expected to focus on Botswana after a diamond that was unearthed from Orapa mines has the scientific community in the Unites States talking not because of its size or colour but its mineral composition.
 
In a brief report that was published by the University of Nevada, Las Vegas, scientists at the institution said they were surprised to discover that a mineral that shouldn’t exist on earth’s surface was found inside a diamond from Orapa mines.

The study led by University of Nevada Las Vegas (UNLV) described the latest discovery as a “first-ever interior earth mineral discovered in nature” and a “new mineral from earth’s lower mantle (that) surfaced as diamond inclusion” and set the world talking about it. 

The report explains that the UNLV geochemists have discovered the new mineral on the surface of the Earth. 

“There’s just one catch: it shouldn’t be here,” the report says. 
According to the report, the mineral — entrapped in a diamond — traveled up to the surface from at least 410 miles (about 659 kilometers) deep within the Earth’s lower mantle, the area between the planet’s core and crust.
 
“It’s the first time that lower mantle minerals have ever been observed in nature because they usually fall apart before they reach the Earth’s surface, unable to retain their structure outside of a high-pressure environment,” the report says. But in this case, the report says, the diamond’s incredible strength preserved the mineral and made the discovery by scientists possible.

The report further states that “the calcium silicate compound, CaSiO₃-perovskite, showed up as infinitesimal small dark specks in a diamond unearthed from an African mine (Orapa mines) in the 1980s.” 
“For jewelers and buyers, the size, colour, and clarity of a diamond all matter, and inclusions — those black specks that annoy the jeweler — for us, they’re a gift,”

UNLV mineralogist Oliver Tschauner, who led the study which was published on 11th November in the journal Science was quoted as saying. 
He reportedly added: “I think we were very surprised. We didn’t expect this.”

The report revealed that the diamond arrived on the surface decades ago in Botswana via the Orapa mine, the world’s largest diamond mine by area. A gem dealer sold the diamond in 1987 to a mineralogist at the California Institute of Technology in Pasadena, and recently, Tschauner and colleagues, including UNLV geochemist Shichun Huang, got their hands on the diamond and applied a new suite of scientific tools to analyze its interior structure.

“What they found is a new crystalline compound that they named davemaoite after Ho-kwang Dave Mao, an experimental geophysicist who developed many of the techniques that Tschauner and his colleagues use today,” the report says. 
Davemaoite was approved as a new natural mineral by the Commission of New Minerals, Nomenclature, and Classification of the International Mineralogical Association.

“Tschauner believes davemaoite originated between 410 and 560 miles below the Earth’s surface, and its discovery highlights just one of two ways that highly pressurized minerals are found by us in nature: from deep within Earth’s interior or inside meteorites,” says the report.
 
It says in 2014, Tschauner’s discovery of “bridgmanite,” highlighted the latter method.

Suggesting that Botswana could be his first port of call in his ‘future projects’, the report says Tschauner is hopeful that discoveries of more minerals — in larger quantities — are on the horizon, which will allow scientists to model the evolution of the earth’s mantle in greater detail. 

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