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Diamonds Reveal Secrets of the Earth

Diamonds Reveal Secrets of the Earth

Teeny tiny minerals locked inside diamonds tell scientists about Earth’s early history.

Diamonds Reveal Secrets of the Earth

Friday, June 9, 2017 - 11:00

Karin Heineman, Executive Producer

(Inside Science) -- To many people, diamonds are a symbol of eternity, strength and everlasting love. No other gem expresses human emotion more powerfully than a diamond. But these earth-grown, precious and nearly indestructible stones aren’t always sought after for their perfect color, cut and clarity to sit on an adoring finger. Scientists see diamonds in a completely different light -- not all for their beauty and perfections, but for their imperfections.

Steve Shirey is a geologist working with diamonds, but not necessarily pretty diamonds you want on your finger. Locked inside the diamonds he works on are very tiny minerals. He’s learned through his career to be ultra-careful when handling such small things.

“These are small materials. They’re unique specimens. I had a specimen, a beautiful specimen on the stage once, and I sneezed and it was gone,” said Steve Shirey, Carnegie Institution of Washington.

Luckily Shirey has more diamonds left to work with. He’s one of a very select group of people in the world who look at diamonds, not mainly for their intrinsic beauty, but for their faults and imperfections -- called mineral inclusions.

“These are seen as flaws in the jewelry industry and so the gem trade will actually map out these flaws,” said Shirey.

“When we want to pick diamonds for research, we actually look for diamonds with the biggest, best, most fancy inclusions that we can find, because those will be the ones that we want to study for the stories that the mineral inclusions will reveal,” said Shirey.

We see these inclusions, or minerals, as tiny specks sealed within a diamond. Shirey says these preserved mineral fragments hold information that tell stories of Earth’s early history.

“One of the beauties of having diamonds enclosing minerals that come from deep in the Earth’s mantle, is that diamond is almost a perfect container. It has very, very low diffusivity, meaning it’s very good at keeping the surrounding fluids and high-pressure compounds in the mantle from getting into the inclusion and altering it,” said Shirey.

The diamonds Shirey examines come from kimberlite volcanic rock. The rock comes from deep in the earth’s mantle and gets carried to the surface, through a volcanic eruption. During eruptions, kimberlitic magma that contains diamonds shoots rapidly up to the earth’s surface.

When this happens, small amounts of diamonds can be found throughout kimberlite that ends up at the surface.

“The diamonds are very rare even in a diamondiferous kimberlite. So, most of what you’re mining is not diamonds. Diamonds are at a part per billion level in the kimberlite,” said Shirey.

Shirey uses diamonds as a means to sample the earth’s deep mantle. He looks at rare diamonds that contain specific sulfide minerals. He then painstakingly removes these tiny mineral grains -- or inclusions -- and analyzes their contents, to determine ages that can be on the order of billions of years.

“Rocks and minerals have a story to tell us. With regard to diamonds, what we’ve done in many cases is try to relate the place that diamonds grow deep in the keels beneath continents, to the processes by which the continents grew to begin with, or the continents collided during long-ago processes like ancient plate tectonics or ancient continental collision,” said Shirey.

The tiny mineral specks trapped inside a diamond can tell researchers a lot about the temperature and pressure conditions when a diamond formed, as well as about the rocks and fluids it grew from. Plus, from its age scientists can tell if it formed at the same time as its diamond host container.

“So, what we can learn from mineral inclusions in diamonds about the earth is quite profound. So, one of the things that we learn is how and when ancient continental collision like that which occurred during plate tectonic cycles may have begun in a way similar to what we see going on today,” said Shirey.

“What has become more interesting -- a more interesting message for me to get across recently is that the diamonds give us such a great sample of the deep earth that diamonds not only are forever, but they’re telling you unique features about the earth,” concluded Shirey.

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Author Bio & Story Archive

Karin Heineman

Karin Heineman is the executive producer of Inside Science TV.