Kimberlite

In short

Kimberlite is a dark, olivine-rich rock formed hundreds of kilometres below the surface. It erupts to the surface very fast and violently along vertical pipes, carrying up pieces of rock torn from the mantle on the way and, sometimes, diamonds. It is the main source of the primary diamonds mined today, and it is named after the town of Kimberley in South Africa. But not every kimberlite contains diamonds.

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How to recognise it

1. 1

   Fresh “blue ground” is a dark grey-green, heavy, hard rock; in a fine-grained groundmass you can see rounded grains of olivine, garnet and pyroxene and fragments of foreign rock.

2. 2

   Weathered “yellow ground” is yellowish brown and crumbles; at first sight it looks like soil.

3. 3

   It contains indicator minerals that most other rocks lack: reddish-purple pyrope garnet, bright green chromium diopside and black magnesian ilmenite.

4. 4

   Diamonds are far too scarce to be seen with the naked eye in the rock; they occur at a scale of carats per tonne.

Myths and misconceptions

• MythKimberlite always contains diamonds; every kimberlite pipe is a diamond mine.

  FactOf about 6,400 kimberlite pipes known by 2014, only around 900 contain diamonds and about 30 are mined for them. None of the more than eighty kimberlitic dikes in New York has any diamonds.

• MythDiamonds form inside kimberlite or in a kimberlite volcano.

  FactDiamonds form roughly 150-200 kilometres down, mostly more than a billion years ago. Kimberlite magma does not make them; it merely carries them up like a very fast elevator.

Did you know?

Where is it found?

• Kimberley, Northern Cape, South Africa · Type localityThe town that gave the rock its name. The hand-dug “Big Hole” is a kimberlite pipe: between 1871 and 1914 more than 22 million tons of rock were dug out and about 14 million carats of diamonds recovered.
• Premier Mine, Cullinan, Gauteng, South Africa · Major depositA carrot-shaped kimberlite pipe; the 3,106-carat Cullinan, found in 1905, is the largest gem-quality rough diamond ever found.
• Mir pipe, Mirny, Sakha (Yakutia), Russia · Major depositFound in 1955, the pipe left a giant open pit more than 525 metres deep and 1,200 metres across; underground mining began again in 2009.
• Udachnaya pipe, Daldyn-Alakit field, Sakha (Yakutia), Russia · Major depositA kimberlite pipe discovered in 1955, two days after Mir; it was worked as an open-pit mine about 640 metres deep.
• Jwaneng, Southern District, Botswana · Major depositOpened in 1982 on three kimberlite pipes; described as the richest diamond mine in the world by value.
• Orapa, Central District, Botswana · Major depositFound in 1967, the mine sits on two kimberlite pipes that merge near the surface and is the world's largest diamond mine by area.
• Lac de Gras (Diavik), Northwest Territories, Canada · Known localityThe kimberlite pipes lie beneath the shallow water of Lac de Gras; the Diavik mine, which began production in 2003, took diamonds from them.
• Ithaca and the Cayuga Lake area, New York, USA · Historic sourceMore than eighty kimberlitic dikes emplaced about 160-135 million years ago are known; none has yielded diamonds, because they come from the uppermost mantle, too cool for diamonds to be stable.

Locations are approximate to protect sites. Red dots mark places in Türkiye. Open in the big map →