A team of geologists have discovered the origins of Earth’s so-called black diamonds.
In their study in the journal Astrophysical Journal Letters, scientists Jozsef Garai and Stephen Haggerty of Florida International University, together with researchers Sandeep Rekhi and Mark Chance of Case Western Reserve University found that the most primitive origins of black diamonds, also known as carbonado diamonds were from inter-stellar space.
For their study, the team used infrared synchrotron radiation at Brookhaven National Laboratory to discover the diamonds' source.
"Trace elements critical to an 'ET' origin are nitrogen and hydrogen. The presence of hydrogen in the carbonado diamonds indicates an origin in a hydrogen-rich inter-stellar space,” said Haggerty.
The term 'carbonado' was coined by the Portuguese in Brazil in the mid-18th century; it's derived from its visual similarity to porous charcoal. Black diamonds are found only in Brazil and the Central African Republic.
"Conventional diamonds are mined from explosive volcanic rocks that transport them from depths in excess of 100 kilometres to the Earth's surface in a very short amount of time. This process preserves the unique crystal structure that makes diamonds the hardest natural material known,” said Sonia Esperanca, program director in the National Science Foundation's Division of Earth Sciences, which funded the research.
Haggerty said though the geological settings of conventional diamonds were virtually identical, none of them were compatible with the formation of black diamonds.
“Approximately 600 tons of conventional diamonds have been mined, traded, polished and adorned since 1900. But not a single black/carbonado diamond has been discovered in the world's mining fields," Haggerty said.
The new data also supports earlier research by Haggerty, which showed that carbonado diamonds formed in stellar supernovae explosions.
Black diamonds were once the size of asteroids, a kilometre or more in diameter when they first landed on Earth.