How King Charles’ diamonds reveal Earth’s deep secrets

The largest diamonds set to feature in King Charles III’s coronation may have an extraordinary origin story. These gems could potentially be remnants of the ancient ocean floor that drifted deep into the Earth’s interior before resurfacing.

In April 1905, an unassuming cardboard box weighing just over a pound arrived at S Neumann & Co, a mining sales agency in London. However, this was no ordinary shipment. Three months earlier, at the Premier Mine in South Africa, the surface manager stumbled upon a remarkable discovery during a routine 18-foot underground inspection. What initially appeared to be a piece of glass embedded in the rough wall turned out to be a massive 3,106.75-carat diamond, nearly the size of a fist. Remarkably, this colossal gem was not only enormous but also unusually transparent, making it a truly exceptional find.

The Cullinan, renowned as the largest diamond ever found, underwent a remarkable transformation after its discovery. Once polished and cleaved into smaller, more manageable stones, the largest crystal yielded was the Cullinan I, also known as the Great Star of Africa, which shines with a cool, stellar glow.

However, the Cullinan diamonds are not just remarkable for their size and transparency; they belong to a special category called “Clippir” diamonds, which are among the largest and clearest examples ever found. These diamonds are unique stowaways from the deep Earth, the only objects that have made it to the surface without being significantly altered.

Nearly 120 years after its discovery, the original mega-diamond has not been forgotten. The Cullinan’s descendants are now part of the British Crown Jewels, typically housed in the Tower of London and brought out for state events. They will play a prominent role in the coronation of King Charles III, with the Sovereign’s Sceptre containing the Cullinan I and the Imperial State Crown embedded with the Cullinan II.

These diamonds not only captivate with their beauty but also offer insights into the Earth’s interior, as they are the only objects that have made it to the surface from the deep Earth without being transformed beyond recognition.

The upcoming coronation ceremony will feature several lesser-known diamonds from the late Queen Elizabeth II’s personal collection, including the Cullinan III, IV, and V. These gemstones have been reset into a modified version of Queen Mary’s Crown from 1911, which will be placed on the head of Camilla, the Queen Consort, during the ceremony.

However, before the rough Cullinan diamond could be transformed and take its place in history, it needed to be sold, and London was chosen as the most promising location for this. This posed a challenge: how to transport such a valuable stone over 7,926 miles (12,755km) from Johannesburg to London without it being stolen.

Surprisingly, the precious rock was sent by ordinary registered post, costing just three shillings or about 75 US cents at the time (around £11.79 or US$13.79 today). Meanwhile, a replica of the diamond made the long voyage to London by steamboat, placed conspicuously within the captain’s safe and guarded by police detectives as a decoy. Remarkably, both the real diamond and the replica arrived safely at their destinations. After years of failing to sell, the real Cullinan diamond was eventually purchased by the Transvaal government for £150,000 (£20m or US$22.5m today) and gifted to King Edward VII.

Clippir diamonds are not mere jewels but rather intriguing geological anomalies that offer a glimpse into the Earth’s mysterious interior. These gemstones are essentially capsules from a world far beneath the surface, characterized by unfathomable pressures, swirling green rock, and elusive minerals. For decades, scientists worldwide have been studying these diamonds to unravel the secrets of this enigmatic region.

Interestingly, the diamonds we value most have the most unusual stories to tell. The largest examples, like the Cullinan diamond, are transforming our understanding of the Earth’s interior. In 2020, Evan Smith, a gemologist at the Gemological Institute of America (GIA), had an unusual opportunity to examine a diamond worth almost as much as a small country. Weighing 124 carats and about the size of a walnut, this diamond possessed wondrous brilliance.

To access this diamond, Smith had to navigate through stringent security measures, including iris scans, identity checks, multiple locked doors, secure lifts, and restricted corridors. While examining the diamond under a microscope, video cameras streamed a constant view of the room to watchful security guards, underscoring the diamond’s immense value and the precautions taken to safeguard it.

The examination of diamonds by researchers is a complex and challenging process, particularly when dealing with high-value specimens. Researchers like Smith, a scientist at the Gemological Institute of America (GIA), aim to study inclusions and chemical traces within diamonds to unravel the mysteries of their formation and the conditions deep within the Earth’s interior.

However, accessing large and valuable diamonds for scientific research is a significant hurdle. These precious gems are often transported globally to potential buyers, but rarely to scientists. Maya Kopylova, a mineral exploration professor at the University of British Columbia, highlights the difficulties researchers face in obtaining diamond samples. Most of the diamonds she works with would have otherwise been discarded, as companies are reluctant to provide valuable specimens, especially those larger than 6mm (0.2 inches), to researchers.

Even when researchers manage to secure diamond samples, the process is convoluted and expensive. Kopylova must visit high-security facilities to identify the desired specimens, and once approved, navigate the paperwork and certification requirements. All diamonds must be accompanied by a Kimberley Process certificate, which verifies their provenance and helps prevent the entry of conflict or “blood” diamonds into the market.

The challenges faced by researchers in accessing and studying diamonds, particularly those of significant size and value, underscore the complexities and limitations of scientific exploration in this field.

The situation of Smith at the Gemological Institute of America (GIA) is unique. He has access to one of the largest collections of diamonds on the planet, with millions of gems sent there for valuation, insurance, or sale. Smith notes that this is the perfect place to study rare and unusual diamonds, as new specimens arrive regularly, allowing him to borrow and examine them for short periods.

A few years ago, Smith and an international team of scientists took advantage of this opportunity by requisitioning 53 of the largest, clearest, and most expensive diamonds available, including some from the same mine as the famous Cullinan diamond. They examined these diamonds under a microscope and made a revolutionary discovery.

Nearly three-quarters of the diamonds contained tiny pockets or “inclusions” of metal that had avoided rusting, which is unusual in ordinary diamonds. The remaining 15 contained a type of garnet that only forms within the Earth’s mantle, the layer above the molten core.

These inclusions provided chemical clues that the diamonds could only have formed at depths between 360 km (224 miles) and 750 km (466 miles) below the surface. This “Goldilocks zone” is deep enough to explain the metal inclusions that were not exposed to oxygen, which is abundant at higher levels, but not so deep that the garnet rocks would have broken down under the immense pressures of the lower mantle. In contrast, ordinary diamonds originate much closer to the surface, just 150-200 km (93-124 miles) below the crust.

The study conducted by Steven B. Shirey and Wuyi Wang on the 124-carat diamond provides insightful information about the formation and journey of these precious gemstones. Their analysis revealed that this particular diamond formed at an exceptional depth of at least 660 kilometers (410 miles) below the Earth’s surface, which is at the deeper end of the possible range for diamond formation.

Diamonds are unique among rocks as they originate from depths far greater than any other materials found on the Earth’s surface. While magma can reach us from around 400 kilometers (249 miles) down, diamonds emerge unchanged from depths of up to 600 kilometers (373 miles), offering a rare glimpse into the Earth’s interior.

Furthermore, every natural diamond, except those grown in laboratories, is at least 990 million years old, with some being truly ancient, having crystallized as early as 3.2 billion years ago when the planet may have been entirely covered by oceans.

The journey of a diamond from its formation to the surface is a remarkable process. It involves the natural movement of super-heated rock in the mantle, which can bring the diamond closer to the surface over hundreds of millions of years. Subsequently, the diamond must be in the right place at the right time to be blasted up in magma, which solidifies into kimberlite rock within the Earth’s crust, where the gemstones may be discovered millions of years later.

This informative study highlights the unique properties and incredible journey of diamonds, providing valuable insights into the Earth’s geological processes and the formation of these captivating gemstones.

The Cullinan diamond is a remarkable gemstone with a fascinating history. After its safe arrival in London, the massive rough diamond was sent to Joseph Asscher for cutting. The sheer size of the rock was so immense that the first strike of the hammer broke the knife and caused Asscher to faint. However, he eventually succeeded in dividing the diamond into nine major stones, with the largest weighing an impressive 530.20 carats, along with 96 smaller fragments. While the larger stones became part of the British Crown Jewels and the monarch’s private collection, the smaller pieces were sold to clients worldwide.

In the 1980s, geologists began to notice differences among diamonds, with some containing minerals that suggested formation at higher pressures than regular diamonds. This observation led to the speculation that certain diamonds might have formed deeper within the Earth’s mantle. Concurrently, researchers noticed a puzzling pattern: most diamonds (Type I) contain significant amounts of nitrogen, affecting their crystal structure and imparting a pale yellow or brown hue. However, a rare subset called Type II diamonds have almost no detectable traces of nitrogen. Interestingly, this phenomenon is extremely uncommon, except in the case of the largest diamonds like the Cullinan.

The discovery of exceptionally large and high-quality diamonds, known as type II diamonds, has been a subject of intrigue and scientific investigation. According to Smith, these diamonds possess unique characteristics that set them apart from ordinary diamonds, making their occurrence a rarity.

Initially, scientists were perplexed by the existence of these exceptional diamonds, as they should have been exceedingly rare. However, through extensive research, they uncovered that some diamonds originate from much deeper within the Earth’s mantle, a phenomenon referred to as “super-deep” diamonds.

Interestingly, a handful of mines, including the renowned Cullinan mine in South Africa and the Letseng mine in Lesotho, have been identified as prime sources for these super-deep diamonds. Smith’s 124-carat specimen, for instance, originated from the Letseng mine.

For decades, most super-deep diamonds discovered were small and lacked significant value. Studying large, expensive diamonds has been a challenge due to their rarity and cost. Consequently, the possibility of these high-quality diamonds being classified as super-deep was not initially considered. As Smith explains, “We never really thought of them as something that could be gem quality – that we would ever be wearing super-deep diamonds or, you know, putting them in crowns or sceptres or anything like that.”

The 2020 study by Smith reached a significant milestone with the discovery of an elusive mineral found in a 4.5 billion-year-old meteorite that impacted Earth in 1879. This ancient extraterrestrial rock, known as the Tenham meteorite, is believed to have originated from a larger celestial object, an asteroid, which experienced a catastrophic impact, causing it to break apart.

During this process, the meteorite endured staggeringly high pressures, similar to those found within the Earth’s interior. As it fell towards Earth, the Tenham meteorite broke up, scattering fragments across Queensland, Australia. Many of these fragments were collected and eventually gifted to the British Museum in London by a geologist’s widow.

Fast forward 143 years, and these fragments have been extensively studied, providing valuable insights into the Earth’s interior composition and conditions. The presence of this elusive mineral in the ancient meteorite serves as a crucial piece of evidence in Smith’s research, offering a rare glimpse into the extreme environments found deep within our planet.

The discovery of the mineral bridgmanite within an alien rock in 2014 provided scientists with a rare glimpse into the Earth’s lower mantle, the layer above the molten core. Bridgmanite is the most abundant material on Earth, but it can only exist under the immense pressures found in the lower mantle. When brought to the surface, it breaks down, making this the first time it had ever been observed.

Remarkably, the 124-carat gem studied by scientists contained this very mineral, albeit in its broken-down form, suggesting that the diamond formed within the lower mantle at pressures at least 240,000 times greater than those at sea level. This equates to 240 times the crushing pressure found in the deepest part of the ocean, the Mariana Trench.

This discovery highlights the unique nature of super-deep diamonds and their potential to provide valuable insights into the extreme conditions and processes occurring within the Earth’s lower mantle, a region that remains largely unexplored and poorly understood.

According to Smith, the exceptional qualities of the world’s largest and most valuable diamonds can be attributed to their unique formation process. While the origins of regular diamonds remain somewhat enigmatic, they are believed to originate from ancient seawater trapped deep underground, along with sinking oceanic plates. This mineral-rich water, potentially due to sudden changes in temperature or pressure, rejects the dissolved carbon, which then crystallizes into diamonds under immense pressures beneath the Earth’s crust.

However, super-deep diamonds like the Cullinan have a different origin. Instead of forming from water, these diamonds begin as carbon dissolved within liquid metal, far deeper in the planet’s interior. Smith explains, “It’s like molten iron nickel alloy with sulphur and carbon dissolved in that. So it’s a totally different kind of fluid, but it’s still carbon fluid. It’s undergoing whatever chemical or temperature changes, and that’s causing carbon to crystallise out.” This initial fluid contains less nitrogen, resulting in diamonds with higher transparency and fewer impurities.

Clippir diamonds are fundamentally different from regular diamonds due to their remarkable size and transparency, which result from the unusual way they form deep within the Earth. Their discovery has revealed some of our planet’s closely guarded secrets about the subduction process when oceanic tectonic plates sink into the Earth’s interior.

Many of the Crown Jewels originate from countries colonized by the British, leading to controversies and calls for their return, such as the Cullinan diamonds from South Africa. The Koh-i-Noor diamond, also of super-deep origin and mined in India centuries ago, has a complex history passing through various rulers before being acquired by Queen Victoria. It will not be featured at King Charles III’s coronation.

These super-deep diamonds provide valuable insights into the Earth’s internal processes, particularly the subduction of oceanic plates, according to experts. Their unique formation and origins make them scientifically significant beyond their rarity and beauty.

The phenomenon we learn about in school classes is the Earth’s division into seven tectonic plates that “float” on the surface, generating earthquakes when they rub against one another and volcanoes when they move apart or get too close. Crucially, while new plates are constantly being formed, some are also slowly slipping below the crust, never to be seen again.

Although scientists have long suspected that these vanished, subducting plates – which are usually heavier, oceanic ones – eventually drift down into the lower mantle, this has never been confirmed. As Smith explains, “You can go to a volcano and say, ‘yeah, this magma comes out of the Earth’, or go to spreading centres of the oceans and see that there’s new crust forming… But it’s really difficult to do the opposite and say, what’s going down into the Earth?”

This information provides an informative overview of the tectonic plate process, highlighting the observable aspects of plate formation and volcanic activity, as well as the challenges in directly observing the subduction of plates into the Earth’s mantle.

Koh-i-Noor: The ‘Cursed’ Diamond Set into the Crown Jewels

Super-deep diamonds offer invaluable insights into the Earth’s interior. These diamonds are believed to be formed from the remnants of tectonic plates that have been subducted deep into the lower mantle. As Dr. Evan Smith explains, “We’ve seen diamonds that look like they’re essentially pieces of the oceanic crust that have been carried down to the lower mantle. These diamonds are physically telling us that this process is physically true.”

Beyond confirming the fate of oceanic plates, super-deep diamonds also provide clues about the composition of the lower mantle. Their existence indicates the presence of carbon, but a recent discovery of a rare super-deep diamond from Juína, Brazil, suggests that there may be vast “oceans” of water in the lower mantle as well. This diamond contains a pocket of vivid blue hydrous ringwoodite, a high-pressure form of olivine that contains around 2.5% water.

Under the microscope, this hydrous ringwoodite appears as a tiny shard of indigo glass, offering a glimpse into the potential water reservoirs that may exist deep within our planet’s interior. Super-deep diamonds serve as unique messengers from the Earth’s depths, providing invaluable information about the composition and processes occurring in the lower mantle.

The Earth’s water cycle has long been a subject of scientific inquiry, with researchers believing that all surface water ultimately originates from the mantle. However, the exact location where this water is stored has been a matter of debate, particularly due to the limited water storage capacity of olivine, a common mineral in the mantle.

Recent discoveries have shed light on this mystery, revealing that water is stored in the form of water-saturated ringwoodite, a high-pressure mineral found in the same region where many super-deep diamonds are formed. This finding suggests that water is stored deeper in the Earth’s interior than previously thought.

Interestingly, these super-deep diamonds have proven to be invaluable not only for their monetary value but also for their ability to provide insights into the Earth’s internal processes. By studying the inclusions and impurities trapped within these diamonds, scientists can gain a unique window into the conditions and processes occurring deep within the Earth’s mantle.

While handling these extraordinary gemstones, researchers often experience a sense of awe and fascination, tempered by the realization that these diamonds are worth millions of dollars. This duality presents a unique challenge, as the scientific desire to study these samples in greater detail is balanced against the need to preserve their immense value as gemstones.

Diamonds in their natural, uncut state possess a captivating allure that often goes unnoticed. Unlike their polished counterparts, rough diamonds emerge from the Earth’s depths as rugged, unrefined rocks devoid of the characteristic sparkle we associate with gemstones. However, their surfaces tell a fascinating story of their geological journey, etched with intricate patterns and unusual shapes sculpted by the forces of nature over millions of years. These natural formations, created by chemical interactions with magma and other subterranean processes, are truly unique and hold a raw beauty that celebrates the diamond’s origins and the incredible forces that shaped it. Appreciating the inherent charm of rough diamonds offers an alternative perspective that values the natural history and authenticity of these precious gems.