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Diamonds Are Forever!

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Wade Hampton III

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Diamonds Are Forever!

PostThu May 30, 2019 2:19 am

It's been said that diamonds are forever — probably because "diamonds
are billion-year-old mutant rocks exposed to many lifetimes of crushing
pressures and scorching temperatures in Earth's deep mantle" doesn't
have the same snappy ring to it.

Diamonds, such as this one (below) have been recreated in a high-pressure,
high-temperature experiment, suggesting that many of Earth's diamonds
form when the mantle crushes ancient seabed minerals.
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Not Just For Girls
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It has been said that diamonds are forever — probably because "diamonds
are billion-year-old mutant rocks exposed to many lifetimes of crushing
pressures and scorching temperatures in Earth's deep mantle" doesn't
have the same snappy ring to it. Either way, it takes a long, long time
for a chunk of carbon to crystallize into a sparkling diamond — so long,
in fact, that scientists aren't positive how they're made. One popular
theory maintains that many diamonds form when slabs of seabed (part of
an oceanic plate) grind underneath continental plates at so-called
tectonic subduction zones. During the process, the oceanic plate and
all the minerals at the bottom of the sea plunge hundreds of miles
into Earth's mantle, where they slowly crystallize under high
temperatures and pressures tens of thousands of times greater
than those on the surface. Eventually, these crystals mix in
with volcanic magma called kimberlite and burst onto the planet's
surface as diamonds.

Support for this theory can be found in the oceanic minerals that give
blue stones — like the infamous (and possibly cursed) Hope diamond —
their signature hue.
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Hope Diamond
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However, these diamonds are among the deepest, rarest and most expensive
on Earth, making them hard to study. Now, research published today
(May 29) in the journal Science Advances provides fresh evidence for
diamonds' oceanic origins.

For the study, the researchers looked at the salty sediment deposits
inside a much more common class of stone, known as fibrous diamonds.
Unlike most diamonds that end up in wedding paraphernalia, fibrous
diamonds are clouded with little deposits of salt, potassium and other
substances. They're less valuable to jewelers, but arguably more valuable to
scientists looking to uncover their underground origins. "There was
a theory that the salts trapped inside diamonds came from marine seawater,
but it couldn't be tested," Michael Förster, a professor at Macquarie
University in Australia and lead author of the new study, said in a
statement.

So, short of tracing the ancient origins of an actual diamond, Förster
and his colleagues attempted to re-create in their lab the hyperhot,
hyperpressurized reactions that occur when seafloor minerals subduct
into Earth's mantle. The team placed marine sediment samples into a
container with a mineral called peridotite, which is a volcanic rock
widely present at depths where diamonds are thought to form; then,
they exposed the mixture to a combination of intense heat and pressure
conditions that mimicked those found in the mantle.
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Not Just For Her
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The researchers found that when the mixture was subjected to pressures
of 4 to 6 gigapascals (40,000 to 60,000 times the average atmospheric
pressure at sea level) and temperatures between 1,500 and 2,000 degrees
Fahrenheit (800 to 1,100 degrees Celsius), salt crystals formed with
nearly identical properties to those found in fibrous diamonds. In
other words, when the old seabed slips into the deep crucible of the
mantle, the colliding forces create the perfect conditions for diamond
formation. (Gem diamonds, which are made of pure carbon and don’t
include any sediment deposits, can also be created this way.)

"We knew that some sort of salty fluid must be around while the diamonds
are growing, and now we have confirmed that marine sediment fits the
bill," Förster said. He added that the same experiments also produced
minerals that are key to the formation of kimberlite, on which diamonds
typically hitch a ride to Earth's surface during volcanic eruptions.
So, diamonds may truly be bits of ancient oceanic history you can wear
on your finger. And if these gems are too expensive for your taste, don't
fret— you can still wear a piece of the planet's extreme past by slipping
on a gold or platinum ring. According to a recent study in the journal
Nature, trace amounts of the shiny minerals in those common types of
jewelry probably originated with an epic neutron star collision that
literally rained bling on our solar system 4.6 billion years ago.

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