Diamond ‘imperfections’ can provide information about their formation and the Earth’s structure. Photo: Istockphoto.

How an imperfect diamond led to a perfect scientific discovery

By Maya Kopylova, UBC Department of Earth, Ocean and Atmospheric Sciences

The value of diamonds is determined by how big, bright and flawless they are. But these aren’t the most valuable diamonds to me. When I look at diamonds, I’m hunting for inclusions — mineral imperfections caught deep within the diamond like a mosquito stuck in amber. Just like the mosquito in Jurassic Park contained the DNA of long-extinct dinosaurs, mineral imperfections in diamonds contain valuable information about where the diamonds came from and how they formed. Inclusions can tell us the story of a diamond’s life.

Close-up, diamond inclusion. Photo: Maya Kopylova/UBC.

In May of 2014, I set out to South Africa to go diamond inclusion hunting, hoping to uncover nature’s perfect diamond recipe. I arrived in Kimberley, South Africa to visit a diamond sorting facility. It sorts diamonds for many mines, including the Cullinan mine. The Cullinan Mine is known for producing some of the world’s biggest and most expensive diamonds. It became famous in 1905 when the largest diamond ever found was discovered there — a diamond now owned by the Queen of England.

The Cullinan mine in South Africa. Photo: Petra Diamonds.

The diamond sorting facility is an imposing building, specially designed for viewing diamonds. The building is long and narrow, with tall slanted windows that prevent the sun from changing the colour of diamonds or otherwise interfering with viewing. Diamonds from many mines in Africa are brought to the centre to be inspected, sorted, appraised, divided into parcels, and shown to potential buyers.

Every morning I’d arrive at the centre, and a security officer would wheel in a cart full of diamonds. I’d spend my days sorting through them, selecting about 300 tiny stones, ranging from one to five millimetres across. Upon my return to UBC, I waited patiently as the chosen diamonds went through a lengthy, multi-border shipping process that ensures diamond shipments don’t fund conflicts or civil wars. When they arrived, my post-doctoral fellow Nester Korolev polished the diamonds before inspecting them for what look like little dust specs — mineral inclusions. These inclusions are sometimes only 10 microns across, just a little bit bigger than a red blood cell.

The mantle is the layer where diamonds form. Photo: Istockphoto.

Inclusions are like little bubbles of non-diamond minerals stuck under the surface of the gem. Diamonds, which form as deep as 700 kilometres below Earth’s surface in a layer called the mantle, are carried toward the surface by molten rock and then emplaced in carrot-shaped underground volcanoes. Diamonds with inclusions can burst when they violently hurtle towards Earth’s surface.

In many instances, diamonds can get the “bends” — much like when a diver swims upwards toward the surface too quickly. In humans, bubbles of CO2, which occur naturally in blood, begin to expand as divers swim to the surface. Eventually, if a diver isn’t careful, the bubbles burst, damaging the lungs and tissues. In diamonds, it’s the inclusions that can rupture, exploding the diamonds well before they reach the surface. That’s why it’s rare to find inclusions, especially ones that formed so deep in Earth’s surface.

Close-up, diamonds and their inclusions. Photos: Maya Kopylova/UBC.

In one of our diamonds, Nester found a small inclusion which contained a mineral never seen before in nature. It’s exciting enough to find a new mineral — only about 5,000 or so are known. Compare that to the 1.8 million known plant, animal, and microbial species, and finding a new mineral sounds even more impressive!

That’s why we were so excited to find calcium silicate (CaSiO3) in a perovskite crystal lattice in our diamond. But finding CaSiO3 turned out to be much more important than just the discovery of a new mineral.

CaSiO3 in a perovskite crystal lattice was previously predicted to exist in nature but had never been found before. Using a high-pressure machine, a device capable of creating pressures only found 700 kilometres below Earth’s surface, scientists were able to make CaSiO3 perovskite and predicted it would exist deep below our planet’s surface. Because it contains calcium, CaSiO3 must have been formed somewhere calcium rich. On Earth, that means the crust, our planet’s outer layer. But because CaSiO3 can only be formed at pressures found 700 kilometres deep this implies the crust must have subducted — forced below another piece of Earth’s outer layer to a depth of 700 kilometres. That was also a new discovery.

The diamond with explosed inclusion of CaSiO3 perovskite. Photo: Maya Kopylova/UBC.

After days of sorting through diamonds for imperfections, we found our mosquito. It didn’t contain nature’s perfect diamond recipe like I hoped it would, but that’s what makes sorting through diamonds worth it. Very often, scientists set out to study one thing, only to change course midway after an unexpected, exciting result sways us in a different direction.

That’s what makes the scientific journey so thrilling.

Maya Kopylova. Photo: Maya Kopylova/UBC.

Learn more

CaSiO3 perovskite in diamond indicates the recycling of oceanic crust into the lower mantleNature 2018.

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