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Outer space may
also 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.
They are unusual
for being the color of charcoal and full of frothy bubbles. The diamonds,
which can weigh in at more than 3,600 carats, can also have a face that looks
like melted glass. The largest diamond ever found was a carbonado from
Brazil; named Sergio, the stone weighed 3,167 carats.
A
rough black diamond
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 been 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.
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?
Now a team led by
geologist Stephen Haggerty of Florida International University in Miami has
presented a new study suggesting that the odd stones were brought to Earth by an asteroid billions of years ago.
The scientists
exposed polished pieces of carbonado to extremely intense infrared light. The
test revealed the presence of many hydrogen-carbon bonds, indicating that the
diamonds probably formed in a hydrogen-rich environment—such as that
found in space.
Stephen Haggerty had an idea why no crater associated with carbonados was
found. The 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.
The most
famous of black diamonds: The
Spirit Of De Grisogono
All
famous diamonds
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