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Diamonds are not just considered a woman's best companion. They’re also highly valued by geologists. These extraordinary gems often house rare or hidden elements that unveil some of the deepest mysteries locked within our planet.
Through studying diamond discoveries, researchers have been able to make educated guesses about what lies beneath Earth's surface and even uncovered insights into our planet’s past. In certain rare cases, these diamonds originate from outer space.
10. Ringwoodite
Scientists propose the existence of an ocean within the Earth's mantle. This ocean resides in a green mineral known as ringwoodite, which can only be found between the lower mantle and the transition zone, located 515 kilometers (320 miles) beneath the Earth's surface. The transition zone lies between the upper and lower mantle.
Ringwoodite cannot exist on the surface as it can only be created under the extreme pressures found deep within the Earth. Scientists have encountered it a few times, but it always changes into a different form when the massive underground pressures are removed. However, geochemist Graham Pearson was able to isolate ringwoodite in its natural state.
The ringwoodite was trapped inside a diamond discovered in a mine in Juina, Brazil. Pearson and his team hypothesized that it was brought to the surface during an earthquake. The discovery was serendipitous; Pearson was actually attempting to date the diamond when he realized it contained ringwoodite.
9. Calcium Silicate Perovskite
Paradoxically, silicate perovskite is one of the rarest minerals despite being the most abundant mineral on Earth. Scientists estimate that 38 percent of Earth's volume is made up of silicate perovskite. Yet, it is so seldom encountered that the first sample we obtained came from a meteorite thought to have originated from another planet. We can't access Earth's silicate perovskite because it is confined to the mantle.
This changed when researchers discovered a stable sample of the mineral inside a diamond found just 1 kilometer (0.6 miles) beneath the surface at the Cullinan Diamond Mine in South Africa. The mineral in question is calcium silicate perovskite (CaSiO3), believed to be the fourth most abundant mineral on Earth.
Interestingly, the diamond containing the sample is one of the rarest types on Earth. It forms only around 700 kilometers (435 miles) beneath the surface, where pressures are 240,000 times higher than at ground level. Scientists believe the calcium silicate perovskite sample became trapped inside the diamond as it was forming.
8. Ice
As previously mentioned, scientists have proposed the idea of an ocean existing within the Earth’s mantle. They theorize that this ocean was formed when water from the Earth's surface oceans was pulled underground by sinking sections of the Earth's crust.
While it is known that the Earth’s crust continues to sink into the mantle, scientists are unable to determine how long this process has been ongoing or the exact size of this ocean. For all we know, it may not exist at all. However, recent findings have provided evidence that suggests the presence of this ocean.
In March 2018, it was reported that scientists had discovered ice samples trapped within diamonds formed deep inside the Earth’s mantle. These scientists believe the ice originated from water dragged into the mantle. This discovery is intriguing because the interior of the Earth is extremely hot, and ice typically cannot form in such high temperatures.
This ice, referred to as ice-VII, only forms between 610 and 800 kilometers (379 to 497 miles) underground, where the pressure exceeds 24 gigapascals. To date, three samples of ice-VII have been found inside diamonds—two from mines in South Africa and one from a mine in China.
7. Liquid Metals
The largest diamonds ever discovered were formed deep within the Earth's mantle, at depths ranging from 322 to 805 kilometers (200 to 500 miles) below the surface. These diamonds often contain impurities, which are metals found within the mantle. Scientists examine these diamonds to gain insights into the composition of the mantle.
Through the analysis of 53 such diamonds, researchers have revealed that the Earth's mantle is rich in iron and nickel, with trace amounts of methane, hydrogen, and garnet. Interestingly, no oxygen was detected, which challenges the belief that the mantle contains significant amounts of oxygen.
6. Harzburgitic Inclusions
Harzburgitic inclusions are a type of rock you may not be familiar with. They belong to the peridotite rock family, which is the most common rock found in the Earth's mantle. Due to their widespread presence in the mantle, scientists often use harzburgitic inclusions found within diamonds to date the diamonds themselves.
Researchers at Vrije University in Amsterdam made an intriguing discovery when they dated 26 diamonds that contained harzburgitic inclusions. Nine of these diamonds were formed around three billion years ago, during a time when a large continent split into smaller ones, creating superheated conditions deep within the Earth.
They found that 10 of the diamonds were only 1.1 billion years old, which is relatively young in Earth's timeline. In fact, this was the first time scientists had come across diamonds of this age. Typically, diamonds are much older, as Earth was far too hot to produce diamonds just one billion years ago.
However, scientists believe that a massive volcanic eruption in what is now Zimbabwe supplied the necessary heat to form these younger diamonds. Their findings open new perspectives on diamond mining, as miners frequently test the age of harzburgitic inclusions in potential mining sites.
5. Boron Molecule
Typically, a diamond's value is influenced by its carat weight—larger diamonds generally cost more. However, the diamond's color (which is a result of other minerals present within it) also plays a significant role in determining its price. The rarer the color, the higher the price. Blue diamonds are the second rarest and thus, quite costly. (Red diamonds are the rarest.)
In 2016, the 24.18-carat Cullinan Dream blue diamond fetched over $23 million at auction. Blue diamonds are considered rare because they form at the deepest levels of the Earth, deep within the lower mantle between 410 and 660 kilometers (250 to 410 miles) underground. For comparison, typical diamonds are formed much shallower, between 150 and 200 kilometers (90 to 125 miles) below the surface.
Blue diamonds get their color from the presence of boron, which is an uncommon element deep within the Earth. Most of the world's boron is found on the Earth's surface, particularly in the oceanic crust. This raises the question: how did boron end up so deep in the lower mantle and even in the second-rarest diamonds on Earth?
While scientists are still unsure, they hypothesize that boron is carried underground when a denser tectonic plate is forced beneath a less dense one. The boron present on the denser plate travels down with methane, hydrogen, and ocean water, eventually reaching the depths where blue diamonds are formed.
4. Kyanite
Although quite rare, diamonds occasionally contain another precious gemstone inside, such as ruby or kyanite. While diamonds typically appear blue when they contain boron, they can also take on a blue hue if they house kyanite.
Kyanite can appear in a variety of colors including gray, green, orange, white, yellow, or even colorless. Among these, blue kyanite is the most valuable, although white kyanite is actually rarer. Occasionally, dishonest sellers may try to pass off blue kyanite as the more expensive blue sapphire.
3. Ferropericlase
It’s uncommon to come across diamonds formed deep within the Earth’s mantle, but researchers at the Gemological Institute of America (GIA) believe they may have discovered some. These diamonds contain ferropericlase, a mineral that resides far within the mantle of our planet.
Diamonds that contain ferropericlase are easily identifiable because of their iridescent quality. They change colors based on the angle from which they are viewed, much like light passing through a soap bubble. The exact cause of this phenomenon remains unclear, but the presence of fluid or magnesioferrite might explain it.
However, not all diamonds with ferropericlase show color shifts. Some are simply transparent brown. Additionally, finding ferropericlase in a diamond isn’t definitive proof that the stone came from the mantle, as these diamonds could also form higher up in the Earth where silica is scarce.
2. Carbon-12
In 1983, a group of researchers from Curtin University in Australia discovered 22 diamonds within zircon crystals from Jack Hills in Western Australia. Upon studying these diamonds, they found that they were made of carbon-12, or light carbon. This was a groundbreaking find because diamonds with significant amounts of carbon-12 typically form only in the presence of living organisms.
The scientists determined that these diamonds formed 4.2 billion years ago, while the zircons themselves were created 4.4 billion years ago. This discovery challenged the belief that single-celled organisms first appeared billion years ago, indicating that these organisms likely existed during the Hadean eon, a full 700 million years earlier than previously thought.
At the time, Earth was an inhospitable environment, even for the most basic forms of life. The planet was sweltering, and its oceans were filled with molten magma rather than water. Scientists speculate that if the carbon-12 wasn’t created by living organisms, it could have been brought to Earth by meteorites.
1. Mutated Carbon Atoms
Carbon exists in three primary forms: diamond, graphite, and buckminsterfullerene. Yet, scientists have identified two additional forms that feature mutated carbon structures, making them even harder than diamond. Remarkably, these unique crystals were predicted long before they were discovered.
These superhard crystals didn’t originate on Earth, but rather from the ureilite-class Havero meteorite that landed in Finland in 1971. Meteorites of this type typically contain graphite and diamond.
It’s believed that these superhard crystals were originally graphite. When the meteorite entered the Earth's atmosphere, the intense heat triggered a chemical reaction, altering the carbon atoms and forming these incredibly hard crystals.
Unfortunately, scientists couldn’t determine the exact hardness of these crystals as they were too small for testing. However, it was clear that they surpassed diamond in hardness, as they couldn’t even be polished using diamond paste.
