Deep within the bowels of the Earth, workers are toiling away in one of South Africa’s most famous diamond mines. But while it may seem just like any other day in the mine, something extraordinary is about to be found. Something so extraordinary, in fact, that no scientist has ever seen it in nature – despite it being among the most plentiful minerals on the planet.
The world around us might seem very familiar, but that’s not to say it doesn’t hold secrets. Sometimes, those secrets even manage to creep out into the light, and this is one of those cases. It’s a story that delves 400 miles into the Earth, and it’s a tale of jewels and incredible pressure. And, fundamentally, it comes down to the unearthing of something that no scientist had ever laid eyes on before.
It all starts with a diamond. The Cullinan Diamond Mine, also known as the Premier Mine, is among the most famous mines in the world – and for very good reason. For starters, in 1905 a record-breaking diamond was discovered there. Named in honor of the mine’s chairman, the Cullinan Diamond is still the biggest rough diamond of gem quality that has ever been found.
Such was the quality of the precious stone that, perhaps unsurprisingly, it caught the attention of the British royal family. As a result, today parts of the Cullinan Diamond – Cullinan I and the Second Star of Africa – adorn two pieces of the Crown Jewels. Other sections of the stone, meanwhile, are the private property of Queen Elizabeth II. And yet the Cullinan Diamond isn’t the only major discovery that’s been made during the lifespan of the Cullinan Mine. In fact, the mine holds a number of records.
A whopping 25 percent of all the diamonds in the world greater than 400 carats have been found at the Cullinan Mine. And among the collection lies another record-breaker. Yes, the Cullinan Heritage diamond discovered at the site currently holds the accolade of being the most expensive rough diamond ever sold. The stone was put up for sale in 2010 and fetched an incredible $35.3 million at auction. What’s more, the Cullinan Mine is the world’s foremost source of blue diamonds to boot.
But while the Cullinan Mine may have yielded some of the largest and most expensive diamonds in the world, arguably the most important discovery made there has nothing to do with the size or worth of the rock in question. Rather, it concerns something inside one of the precious stones – a mysterious fragment that could well have been a billion years in the making.
You’ve probably never heard of calcium silicate perovskite – and with good reason. After all, the chemical compound is normally only found some 400 miles below the surface. The mineral is, however, believed to be the fourth most bountiful on the planet. And yet up until recently, scientists had never actually managed to see a sample of it in the form that it holds deep within the Earth’s structure.
While most diamonds are formed at between around 90 and 125 miles beneath the surface of the planet, the one at the heart of this story is different. It’s what scientists call a “super-deep” diamond, and by researchers’ best estimates, it took shape in a location more than 430 miles underground. What’s more, this fact is key to the incredibly exciting discovery that lies within the sparkling rock.
You see, the diamond was formed at around the same depth as places where you’d expect to find calcium silicate perovskite. That far below the surface, the pressure is approaching 250,000 times greater than it is at sea level. And as the immense pressure created the gem, it also trapped a tiny piece of the mineral inside.
So, as the diamond subsequently made its way up into the mine, it brought with it a particle of calcium silicate perovskite. And according to Graham Pearson of University of Alberta, the discovery of the mineral is a real landmark.
A professor of geochemistry, Pearson is co-author of a study that has explored the diamond’s mysteries. In a statement quoted by Newsweek, Pearson said, “Nobody has ever managed to keep this mineral stable at the Earth’s surface. The only possible way of preserving [it] at the Earth’s surface is when it’s trapped in an unyielding container like a diamond.” When you look at the numbers concerning calcium silicate perovskite, though, it’s almost incredible that no one had set eyes on it before.
Pearson explained in his statement – this time quoted by The Smithsonian – that there could be “as much as zetta tonnes of this perovskite in deep Earth.” What’s a zetta? Well in simple terms, it’s a one preceding 21 zeros. That, of course, is an enormous amount of perovskite lying deep beneath the surface – and it makes the fact that this is the first time scientists have managed to lay eyes on the mineral even more astounding.
And while scientists have always thought perovskite to be abundant, this more specific estimate has only been possible thanks to the recent discovery at the Cullinan Mine. Indeed, although experts have been trying to study the mineral since the 1960s, perovskite’s unstable nature has thwarted previous attempts.
As far back as 1975, scientists had managed to synthesize perovskite in the laboratory. Studying naturally occurring samples, however, proved all but impossible. Instead, scientists had to utilize something called laser-heated diamond anvil cells to research what happened to the mineral in lower mantle conditions. With this new discovery, though, all of that has changed.
The discovery has led to a whole raft of new ideas and research coming to the surface. One such area of investigation concerns the crust underneath the ocean and how the planet’s carbon cycles work. You see, the perovskite in this case started its journey deep beneath the waves – and then some.
According to Pearson, the chemical components that went into making the mineral began life as part of the ocean crust. “When that gets subducted down in the Earth’s mantle,” he went on to explain in the statement, quoted by National Geographic. “It keeps going until it transforms into higher and higher pressure mineral phases.” Over vast amounts of time, then, the components are made into something else.
This wasn’t the first time that Pearson had helped make a monumental diamond-based breakthrough, either. Back in 2014 he was behind the discovery of ringwoodite – the fifth most plentiful mineral on the planet. It was an important finding – one that indicated the presence of a huge amount of water in the Earth’s mantle.
The story of the calcium silicate perovskite found in the diamond is far from over, though. Hopefully, it won’t be the last amazing discovery made in a precious stone pulled out of the Cullinan Mine. But there’s still a lot of work to do to determine certain things about this most recent find.
For starters, scientists are still unsure as to even the approximate age of the diamond. According to Pearson, the stone could be “quite young [or] a billion years old.” What’s more, this investigation forms just part of a research initiative designed to gather data from diamonds. “We have a program looking at super-deep diamonds with the purpose of obtaining information,” Pearson has explained.
Pearson also suggests that the find in the diamond mine is a brilliant example of just how modern science works. “You build on theoretical predictions – in this case, from seismology – and once in a while you’re able to make a clinching observation that really proves that the theory works,” he has stated. And in this instance, that clinching observation came courtesy of a glittering gem from hundreds of miles under the ground.