How Do Diamonds Form?

After a recent analysis of the royal regalia, more specifically the Cullinan Diamond, scientists believe that the Cullinan Diamond may be a deep or even a super-deep diamond. These findings were presented virtually at this year’s Goldschmidt geochemistry conference. Super-deep diamonds are very rare due to the depth at which they are formed. Diamonds are amongst the most popular gemstones, if not the most popular, but there is still a general lack of knowledge when it comes to its origins and history. But how do diamonds form in the first place and when did they become so prominent?

Diamonds’ molecular structure makes them the hardest substance on the planet. This makes them incredibly sought after in industrial production. Their beauty however and the way the gemstones disperse light is what makes them so attractive and favoured in the jewellery industry. Diamonds have been used for both practical reasons and in accessories since antiquity. 

How Do Diamonds FormMost people know diamonds as the most popular gemstone for jewellery and engagement rings. The tradition to use diamonds for engagement rings dates back to the Romans. This, however, was not due to the beauty of the stone but due to a Roman belief that diamonds possessed abilities to prevent poisonings, repel evil and aid in reconciliation. The custom only became widespread worldwide with the general population in 1938. 

As we know, diamonds are formed under incredible pressure. They are in fact solely made of carbon, the same element that forms graphite. The only difference between the graphite in your pencil and diamonds is the structure in which its atoms are arranged. Diamonds are formed deep in the Earth’s crust, in the mantle. Most of them form at about 150 to 200 km depth, however as mentioned above, some deep and super-deep diamonds like the Cullinan and Hope Diamonds can be formed even deeper between a depth of 400 to 660 km. The extreme conditions of the Earth’s crust apply heat, between 900 to 1300 degrees Celsius, and pressure 50 000 times higher than that of the surface to the carbon atoms. In response, the carbon atoms crystallise forming diamonds. 

Diamonds form at such a depth that we would be unable to mine them, so how do we get access to these precious gems?  Molten kimberlite, or magma, forms under the same conditions as diamonds. After formation kimberlite expands rapidly which causes eruptions. When erupting, the magma carries diamond-bearing rocks with it. The magma moves at incredible speeds which creates a pipe to the surface, known as a kimberlite pipe. This brings the diamonds closer to where we have access to mine them. The reason carbon don’t rearrange itself into graphite when travelling to the surface is due to the speed of the eruption which happens in the span of a few hours. The speed of the eruption and the fast cooling down of the magma ensures the carbon will remain in its diamond form.

Diamonds are by far not the rarest of gems, however, they surely are one of the most beautiful. Ensnaring humanity’s imagination for centuries diamonds have become a symbol of prosperity and luxury. You can check out our range of diamond rings here. What is your favourite gemstone? Let us know in the comments below.