The formation and origins and diamonds (Part 1)
Diamonds are formed from carbon atoms under conditions of extremely high pressure and heat. The formation of the world’s most precious gem from insignificant carbon atoms itself is a miracle of nature. Equally amazing is the way natural diamonds reach the earth’s surface!
Natural diamonds were formed in the mantle of the earth billions of years ago. They typically form 150-200 km below the surface of the earth. Some diamonds, known as ‘superdeep diamonds’, are formed at much greater depths, in the transition zone of the mantle (410-660km below the earth’s surface) or even beyond 660km and as deep as 700km, somewhere in the lower mantle. Under the extreme environment of the mantle, diamonds are formed from carbon atoms through intense heat of between 900°C and 1300°C and at pressures of 45kbar.
Image credit: Wikipedia
So how did the diamonds deep in the earth make their way to the surface? Simply put, diamonds hopped on an accidental ride of rare volcanic eruptions and were transported to earth’s surface in magma.
There are two main types of magma that carry natural diamonds to earth’s surface, of which kimberlite is the dominant type by far. In a kimberlite eruption, the magma surges from the earth’s mantle and carries with it diamonds that were already formed in the depths of the mantle. The magma cools and crystallises into volcanic rocks known as kimberlite. The vertical geological structures formed when the magma erupts through the earth’s crust are called ‘kimberlite pipes’, often the sites of diamond discovery.
Kimberlite is named after the Kimberley region of South Africa, where diamond-rich kimberlite pipes were first found. The eruption of kimberlite magma is thought to be the most rapid and violent type of volcanic eruption on Earth, and such an event had never been witnessed in the history of humans. Some estimates place the last kimberlite eruption at around 40 million years ago.
Image credit: Whiteflash
Although not all kimberlite pipes contain diamonds, such a discovery spurred diamond exploration companies to search for kimberlite pipes as it would be a more likely way to locate diamonds. Countries and regions that have diamond-rich kimberlite pipes have now become famous diamond producers, such as South Africa, Australia, Brazil, Russia, etc. We will be talking more about diamond-producing countries, diamond cutting and trading centres in next month’s blog entry. Stay tuned!
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