Where do diamonds come from?

Diamonds are an ancient, pure carbon ore, and most of them are believed to be between a billion and 3.5-billion-years-old. But where do diamonds come from and where are they formed?

The formation of diamonds

Rough diamonds are formed throughout millions of years at a depth of 150-250 kilometers underground, and rise to the surface of the earth as two types of rocks, kimberlite and lamphorite, which contain, besides diamonds, rubies and other minerals. It is believed that these rocks reach the Earth's surface through small cracks in the Earth's crust caused by volcanic eruptions that occurred in thousands of sites.

Natural diamond kimberlite

What does a kimberlite deposit look like?

 

Kimberlite rocks emerge to the surface vertically and their appearance resembles carrots rising from the ground, showing a large round edge that shrinks the deeper you explore it. These geological structures are called kimberlite pipes and they are the source of diamonds. This is why diamond mines often resemble a cochlea that descends deep into the earth: these are the roads trucks travel along the mines to deliver diamond ore to the surface, where it is processed.

Volcanic-kimberlite funnel

The meaning of the name "Kimberlite"

Kimberlite is named after the South African city of Kimberley, where the kimberlite rock formation was first linked to the discovery of diamonds. In fact, until the early 19th century, the link between kimberlites and diamonds was unknown.

A discovery of a diamond weighing 83.5 carats in Kimberly in 1871, started  the era of modern diamond mining.

Kimberlite diamond mine

Do all kimberlites contain diamonds?

The hunt for kimberlite pipes and diamond deposits is constant. While not all kimberlite rocks contain rough diamonds, their detection is still exciting because of the potential discovery. To date, some 6,400 kimberlite pipes have been discovered around the world, but only 30 of them were found to contain diamonds worthy of the resources invested in a mining operation.

Kimberlite pipes are usually discovered using electromagnetic aerial mapping. Once the distinct round shape of a kimberlite is detected, soil samples are taken and tested to discern the presence of minerals that will indicate the possibility of finding diamonds in the discovered pipe. Still, the presence of diamonds in a kimberlite pipe does not guarantee that it will be developed into a mine as here, economic calculations predict the costs of production versus mining profitability.

kimberlite with diamond

Are diamonds found only in kimberlite pipes?

 

Diamonds can be found in various deposits, not only in kimberlite rocks. Over the course of thousands of years, some pipes have disintegrated and swept away by lakes and rivers into the sea, which is why diamonds are discovered both in riverbeds and at sea. To date, however, the southwest African nation of Namibia is the only site in the world where diamonds have been discovered in the ocean. As diamonds have also been found in Namibian rivers, it is believed that over the years some of them have been washed out to sea.