The black diamonds known as carbonados got their name for their carbonized, or burnt, look.
Outer space may be the birthplace of the mysterious black diamonds known as carbonados. From the Portuguese word for burned or carbonized, carbonados were first found in Brazil in the 1800s and have since turned up elsewhere, most notably in central Africa. Unlike the clear diamonds of engagement rings, which are single crystals, black diamond consists of aggregations of individual crystals, which lend the gem its dark color. The largest diamond ever found was a carbonado from Brazil; named Sergio, the stone weighed 3,167 carats. (One carat equals one-fifth of a gram.)
The origins of carbonados have long baffled scientists. Black diamonds don't adhere to the rules of diamond mineralogy, and they don't occur in the usual places where clear diamonds are found. Even so, scientists initially believed they must have bee fashioned in the same conditions under which clear diamonds are thought to form. That is, they were crafted deep within the Earth, 100 to 300 miles down, when intense heat and pressure transformed carbon into diamonds, which volcanic eruptions then lofted to the surface. But that theory suffered a blow when scientists examined the carbon isotopes of black diamonds. (Isotopes are species of a chemical element that reside in the same place on the periodic table but have different atomic weights and physical properties.) Unlike clear diamonds, black diamonds feature ratios of the two most common carbon isotopes in the Earth's crust -- carbon-12 and carbon-13 -- that characterize surface carbons rather than those found in the Earth's depths.
Did carbonados form in the unimaginably explosive shock waves emitted by dying stars, such as this one shot recently by NASA's Hubble Space Telescope?
This finding helped lead to a new theory of carbonado formation. In 1985, Joseph Smith of the University of Chicago and J. Barry Dawson of the University of Sheffield in England suggested in an article published in the scientific journal
Geology that large meteor impacts in the Precambrian Era (roughly 570 million years ago back to Earth's beginning some 4.5 billion years ago) formed the black diamonds we find today. Scientists had long deemed carbonados quite old, because the streams where they are typically found cut through geologic strata dated from one to more than two billion years old. In fact, recent atomic measurements of black diamonds have placed their origins at nearly four billion years ago, a time when a constant barrage of giant meteors battered the Earth.
In the 1990s, other scientists showed that Brazilian and African carbonados bear similar isotopes of carbon and nitrogen, suggesting a common origin, while still others provided theoretical and physical evidence that black diamonds could have arisen during the extreme shock and heat of a meteor impact. But why, some scientists wondered, had no unambiguous evidence ever been shown for craters associated with carbonados? Geologist Stephen Haggerty of the University of Massachusetts at Amherst had an idea why, and he shared it with a dumbfounded audience at a 1996 American Geophysical Union meeting in Baltimore. Carbonados were born not on Earth, either the way regular diamonds are or by meteor impact, he said. Rather, they originated in dying stars, when shock waves from exploding red giants crushed carbon into dense aggregations of black diamond and sent them hurtling into deep space. Eons later, the Sun's gravity lured some of this material into our solar system, where blocks of it slammed into our atmosphere, shattering into the fragments we find strewn over select areas today, perhaps billions of years after they formed.
This finding helped lead to a new theory of carbonado formation. In 1985, Joseph Smith of the University of Chicago and J. Barry Dawson of the University of Sheffield in England suggested in an article published in the scientific journal
Geology that large meteor impacts in the Precambrian Era (roughly 570 million years ago back to Earth's beginning some 4.5 billion years ago) formed the black diamonds we find today. Scientists had long deemed carbonados quite old, because the streams where they are typically found cut through geologic strata dated from one to more than two billion years old. In fact, recent atomic measurements of black diamonds have placed their origins at nearly four billion years ago, a time when a constant barrage of giant meteors battered the Earth. In the 1990s, other scientists showed that Brazilian and African carbonados bear similar isotopes of carbon and nitrogen, suggesting a common origin, while still others provided theoretical and physical evidence that black diamonds could have arisen during the extreme shock and heat of a meteor impact. But why, some scientists wondered, had no unambiguous evidence ever been shown for craters associated with carbonados? Geologist Stephen Haggerty of the University of Massachusetts at Amherst had an idea why, and he shared it with a dumbfounded audience at a 1996 American Geophysical Union meeting in Baltimore. Carbonados were born not on Earth, either the way regular diamonds are or by meteor impact, he said. Rather, they originated in dying stars, when shock waves from exploding red giants crushed carbon into dense aggregations of black diamond and sent them hurtling into deep space. Eons later, the Sun's gravity lured some of this material into our solar system, where blocks of it slammed into our atmosphere, shattering into the fragments we find strewn over select areas today, perhaps billions of years after they formed.
Reaping the benefits
As for tapping the riches of any diamonds from space, don't hold your breath. Earth-hitting meteorites that either bear or engender diamonds are few and far between, and unlike diamonds you're likely used to, their associated diamonds often cannot be seen, much less admired, with the naked eye. Black diamonds, for their part, are rare and are primarily used for industrial purposes. And the challenges of harvesting any diamonds on Uranus and Neptune, which are roughly 1,700 and 2,720 million miles away from Earth, respectively, are as clear as the Koh-i-Noor diamond. Alas, scientific understanding is the primary beneficiary of diamonds from the heavens.
"Prospecting for Diamonds in the Outer Planets," by Warren E. Leary, The New York Times, 10/5/99. "Giant Black Diamonds Of Mysterious Origin May Hail From Space," by William Broad, The New York Times, 9/17/96. Photos: (1,2) NASA.
