Plenty has been said about how much of outer space, and even the oceans, have been left undiscovered, but what you may not hear about as much is the abundance of undiscovered wonder under the Earth’s surface. Sure, it may not be full of life, but there’s still a great deal to be studied!

The fact of the matter is that most of the fascinating things hiding under our soil can’t be easily studied because exploring the Earth’s center is usually just the work of science fiction. One massive mine in South Africa changed all that! What was discovered in its depths rivals the beauty of any natural wonder above the planet’s surface… and its value, too.

The Cullinan Diamond, found in South Africa’s Premier Mine, is the largest rough diamond of gem quality in the world. A diamond like that might not be ready to be part of jewelry like an engagement ring, but with some polishing it could be!

This discovery was huge news when it was discovered in South Africa in 1905. The British royal family was so enchanted by the Cullinan Diamond that a portion of it was used in the royal crown jewels, and Queen Elizabeth II kept other parts of the stone for her private collection!

Even to this day, of all the known diamonds in the world worth 400 carats or more, as many as 25 percent of them have been found in the Premier Mine. That’s absolutely huge for just one mine out of the many across the globe.

Unsurprisingly, considering its sheer size, the Cullinan Heritage Diamond is also the most expensive rough diamond ever sold, for a whopping $35.3 million in a 2010 auction. Additionally, it’s the world’s largest source of rare blue diamonds.

Just about every rock enthusiast worth their salt knows how valuable diamonds are, but following that initial discovery of the Cullinan Diamond, something else, within the precious stones themselves, made people take notice…

It all started with the chemical compound calcium silicate perovskite, which is usually found over 400 miles below the Earth’s crust. Although it’s actually the fourth most common mineral in the world, throughout most of human history, scientists couldn’t get a good look at it.

At the same time, it’s important to note that the enormous size or staggering monetary value of the massive Cullinan Diamond is hardly the only remarkable thing about it.

You see, diamonds are usually formed naturally anywhere between 90 to 120 miles under the surface of the Earth, but this special diamond started forming around 430 miles under the Earth’s surface, which made a huge difference by the time it was finally discovered in 1905!

The Cullinan Diamond was surrounded by calcium silicate perovskite, and because it was in an environment with pressure roughly 250,000 times that of sea level, by the time it reached the Premier Mine, some of the compounds got trapped inside the diamond, making it more accessible than ever!

Graham Pearson, a geochemistry professor at the University of Alberta, studied the phenomenon closely and knew how groundbreaking it was. “Nobody has ever managed to keep this mineral stable at the Earth’s surface,” he explained in an interview.

Furthermore, the way in which the chemical compound finally became obtainable was unprecedented. “The only possible way of preserving [it] at the Earth’s surface is when it’s trapped in an unyielding container like a diamond,” Graham continued.

Even though it took so long for the compound to be obtained, that doesn’t mean it’s scarce. In fact, Pearson explained that there could be “as much as Zetta tons of this perovskite in deep Earth.” A Zetta ton is a one followed by 21 zeros, so there’s no shortage of perovskite!

Granted, even though they hadn’t gotten their hands on it for so long, scientists long knew there was plenty of perovskite since the 1960s. In fact, even going as far back as the 1970s, scientists had been attempting to synthesize the substance.

Still, nothing compares to studying the real deal, which long seemed impossible. The synthetic material from diamond anvil cells heated with lasers was the best they had to work with, and finally getting their hands on real perovskite opened up exciting new possibilities for research.

For example, with real perovskite scientists can now study the naturally-occurring perovskite to learn more about how carbon cycles deep within the Earth function, as well as investigating the Earth’s crust under the ocean’s surface.

Moreover, perovskite originated in the Earth’s crust. “When that [perovskite] gets subducted down in the Earth’s mantle,” Pearson continued. “It keeps going until it transforms into higher and higher pressure mineral phases.”

Pearson had experience studying a rare material that scientists had previously only dreamed of obtaining because in 2014 he helped lead the discovery of ringwoodite, the Earth’s fifth most plentiful mineral, but another one that exists mostly within the mantle.

As for the Cullinan Diamond, a great deal of work still lies ahead for Graham Pearson and all of the other scientists who have been so eager to study it, and the surprising chemical compound that it carried, for so many years.

Even when it comes to the Cullinan Diamond itself, nobody’s entirely sure how old it even is. Pearson says it may be “quite young [or] a billion years old… we have a program looking at super-deep diamonds with the purpose of obtaining information.”

If nothing else, however, Pearson says this is just one example of how amazing modern science can be. “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.”

It’s pretty amazing that something like this is finally possible. There’s so much more to learn!

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