![]() By meteorite or mantleĪs diamonds crystallize in the immense pressures deep within Earth, they occasionally encapsulate minerals from the planet's mantle, such as deep red garnet or green olivine. It was later cut into its distinctive 55-facet shape-a task that took three years because of the stone’s extraordinary toughness. The diamond was estimated to be more than 800 carats, equivalent to 160 grams, when it was purchased anonymously in the 1990s, according to the seller's representative. As scientists later realized, violent volcanic eruptions blasted these conduits to the surface, dragging the stones now known as kimberlite diamonds from deep underground with a surge of magma.įor the carbonados, Cartigny says, "we're basically back 150 years ago." Without a host rock, scientists can only search for clues in the odd features of the black diamonds themselves-but each one seems to tell a different story.īefitting its name, no one knows exactly where on Earth the Enigma comes from. Answers began to take shape in the 1870s when the diamonds were found embedded in vertical pipes of volcanic rock in the Kimberley area of South Africa. Through the millennia, wind and water have erased most other clues to the black diamonds’ origins, eroding the rocks that the gems formed in and scattering the grains along the shores of ancient rivers.Īround 150 years ago, a similar problem shrouded the origins of the type of diamond that is most commonly mined today, says Pierre Cartigny, a geochemist who specializes in diamonds at the Paris Globe Institute of Physics. Carbonados were most likely deposited when the two landmasses were joined as a single swath for more than a billion years, splitting into the paired locations after Earth's last supercontinent Pangea broke apart starting 180 million years ago. The carbonados at these two locations "are so similar in minute details” that they must be related, says Peter Heaney, a mineralogist at Pennsylvania State University. Decades later, carbonados also turned up in the Central African Republic-the only other place they've ever been found. Black diamonds were discovered in the 1840s by miners in eastern Brazil who named the minerals carbonado after the Portuguese word for burnt or carbonized. The story of these ultra-tough minerals unfolds in two spots on either side of the Atlantic Ocean. "There's no single model that explains everything," says Wuyi Wang, vice president of research and development at the Gemological Institute of America, who certified the Enigma as a natural carbonado. Carbonados have been used as drill bits that can puncture tough rock and with grinding wheels that sharpen tools.Ĭarbonado's many oddities have led to a slew of theories about their origin. Unlike the single crystals of traditional gem diamonds, carbonados are made up of an interlocking network of crystals, which imparts extra resistance to fracturing under pressure and makes them valuable as industrial abrasives. Until recently, though, carbonados were recognized not for their beauty but for their toughness. "This is a pretty honking big diamond," says Thomas Stachel, a mineralogist specializing in diamonds at the University of Alberta. And the Enigma itself is no small rock at nearly the size of a racquetball. ![]() The group includes the hulking 3,167-carat Brazilian carbonado known as Sergio-the largest diamond ever found. They are found in only two regions of the world-Brazil and the Central African Republic-and can grow astonishingly large. Jet black, opaque, and full of visible holes, carbonados have a unique combination of physical and chemical features unlike any other known diamonds. The Enigma and all other carbonado diamonds formed in a mysterious event some 3.8 to 2.6 billion years ago. The sale of this bizarre stone has reignited a long-simmering debate about where it came from, stoked by the controversial theory that it may have arrived from outer space. With a final closing bid of $ 4.28 million, an anonymous buyer just became the new owner of the 555.55-carat black diamond known as the Enigma.
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