Precious gemstones have fascinated humanity for ages, but the mysteries of their formation and ascent to the Earth’s surface have remained a source of intrigue. Renowned mineralogist, Lee Groat, of the University of British Columbia, sheds light on the deepest gemstones known to humanity, with diamonds taking the spotlight for their allure, industrial utility, and scientific revelations.
Diamonds, the object of desire for many, are believed to originate within the Earth’s upper mantle, residing at depths between 93 and 186 miles beneath the Earth’s surface, where pressures exceed an astounding 20,000 atmospheres. The remarkable property of diamonds to crystallize is intricately tied to these extreme pressures. However, the precise mechanisms of diamond formation remain a subject of ongoing research, still shrouded in mystery.
Until recently, another gem, peridot, in its olivine form, was a strong contender for the title of the deepest-occurring gemstone. Olivine constitutes more than half of the upper mantle, stretching down to approximately 255 miles beneath the surface. Yet, in 2016, the discovery of superdeep diamonds originating from around 410 miles below the Earth’s surface resolved the debate surrounding the deepest gemstone.
To determine the depth of these superdeep diamonds, researchers embarked on an extensive study of their crystallization patterns and inclusions. Inclusions of the mineral known as bridgmanite, coupled with iron-nickel-carbon-sulfur melt, provided compelling evidence that these diamonds crystallized in the lower mantle, where pressures can exceed a mind-boggling 235,000 atmospheres.
The remarkable longevity and resilience of diamonds further enhance their allure. Some diamonds on the Earth’s surface are estimated to have formed as far back as 3.5 billion years ago, underscoring their status as ancient treasures. The robust chemical bonds holding diamonds together are the key to their remarkable endurance. Composed of carbon, the transformation of a diamond into graphite only occurs when subjected to temperatures exceeding 1,652 degrees Fahrenheit.
Curiously, the process of extracting diamonds from the depths of the Earth is not a tale of deep excavation but rather one of a unique type of magma: kimberlite. Kimberlite magmas are known for their volatility, erupting at astonishing speeds, dragging diamonds along from the surrounding rock. This explosive journey allows these gemstones, which formed over billions of years, to reach the Earth’s surface in a matter of months or, in some cases, mere hours.
Beyond their aesthetic and industrial value, diamonds harbor invaluable scientific insights about the Earth’s interior and its complex processes. Scientists have harnessed diamonds to unlock secrets about the planet’s formation, the nature of tectonic activity, and the presence of water within the Earth’s mantle. Thus, diamonds remain not only a symbol of beauty but also a source of profound understanding about the natural world that surrounds us.
