Gemstones have captured our curiosity and awe for centuries, but have you ever wondered how these precious stones form and find their way to the surface? According to mineralogist Lee Groat of the University of British Columbia, the deepest known gemstones are diamonds, prized for their beauty, industrial use and scientific importance.
Diamonds are thought to be formed in the upper mantle, between 93 and 186 miles below the Earth’s surface, under intense pressure that can exceed 20,000 atmospheres. Laboratory experiments have shown that diamonds crystallise only under extreme pressure, although the exact process of their formation is still not fully understood.
Until recently, peridot, the gemstone form of olivine, was a strong contender for the title of deepest occurring gemstone. Olivine makes up more than half of the upper mantle, which extends down to about 255 miles. However, in 2016, super-deep diamonds were discovered from around 410 miles below the surface, settling the debate over the deepest gemstone.
Researchers determined the depth of these diamonds by studying their crystallisation patterns and inclusions. Inclusions of a mineral called bridgmanite and iron-nickel-carbon-sulphur melt indicated that these superdeep diamonds likely formed in the lower mantle, where pressures can exceed 235,000 atmospheres.
Diamonds are considered to be incredibly old, with some estimated to have been formed up to 3.5 billion years ago. The strength of their chemical bonds is responsible for their longevity. They are made of carbon, and when a diamond is heated above 1,652 degrees Fahrenheit, it turns into graphite.
Interestingly, diamonds do not have to be mined from deep within the earth. They are brought to the surface by a type of magma called kimberlite, which erupts at incredible speeds, pulling diamonds from the surrounding rocks with it. This process allows gems that have taken billions of years to form to reach the surface in a matter of months or even hours.
In addition to their aesthetic and industrial value, diamonds contain invaluable scientific information about the Earth’s interior and its processes. Scientists have used diamonds to learn about the formation of the planet, tectonic activity and the presence of water in the mantle. These gemstones continue to be valuable not only for their beauty, but also for their contribution to our understanding of the natural world.
