Skip to content
Know.itKnow.it
Create an animated lesson
On request

This article is free to read. Creating a lesson uses your daily or stored credits; review the language and settings before starting.

How do diamonds form?

ScienceLesson on requestFree to read

Quick answer

Diamonds form deep in Earth's mantle where carbon is exposed to pressures over 4.5 gigapascals and temperatures of roughly 1,000°C or more. These conditions force carbon atoms into a cubic crystal lattice. The diamonds are then carried to the surface by rare, deep-source volcanic eruptions that solidify into kimberlite pipes.

Diamonds form when carbon is subjected to extreme pressure and high temperature deep within Earth's mantle, typically 150 to 250 kilometers below the surface. The carbon atoms crystallize into a cubic lattice, and the diamonds are later brought to the surface by volcanic eruptions.

Step by step

  1. Carbon-rich material, such as subducted oceanic crust or ancient mantle, accumulates in the deep mantle.
  2. At depths of 150 to 250 kilometers, pressures exceed 4.5 gigapascals and temperatures of roughly 1,000°C or more, causing carbon atoms to bond into a cubic crystal lattice.
  3. The diamond crystals remain stable in the mantle for millions to billions of years.
  4. A deep-source volcanic eruption rapidly transports mantle rock and diamonds upward through the crust.
  5. The magma cools and solidifies into kimberlite pipes, preserving the diamonds near the surface.

Key things to understand

  1. Carbon, the same element found in graphite and living things, is the raw material for diamonds.
  2. Deep in Earth's mantle, pressures above about 4.5 gigapascals and temperatures around 1,000 °C or more force carbon atoms into a dense cubic crystal.
  3. This crystalline form is diamond, and it is stable only under those extreme conditions; at the surface, diamond is actually metastable.
  4. Diamonds are transported upward by rare, deep-source volcanic eruptions that carry mantle rock, called kimberlite, to the surface.
  5. The magma must cool and solidify quickly enough for the diamond to survive the journey without converting to graphite.

Labelled diagram

  1. Carbon source

    Carbon from subducted crust or mantle rocks collects in the deep mantle.

  2. Mantle conditions

    High pressure and temperature force carbon atoms into a cubic crystal lattice.

  3. Diamond stability

    The crystal remains stable for millions of years under mantle conditions.

  4. Volcanic transport

    A deep-source eruption rapidly carries diamonds upward in magma.

  5. Kimberlite pipe

    The magma solidifies into a pipe, preserving diamonds near the surface.

How diamonds form and reach the surface

Real-world examples

  • The Kimberley mines in South Africa, where the first major diamond pipes were discovered in the 1870s.
  • The Argyle mine in Western Australia, which closed in 2020, was famous for pink diamonds from a lamproite pipe.
  • The Udachnaya pipe in Siberia, Russia, one of the world's largest diamond-bearing kimberlite bodies.
  • The Diavik Diamond Mine in Canada's Northwest Territories, which extracts diamonds from kimberlite beneath a lake.

Common mistake

✗ Myth: Diamonds are formed from coal.

✓ Fact: Diamonds form from carbon in the deep mantle, not from coal, which is a surface deposit of fossilized plant material. Coal has never been found in mantle-derived rocks, so it cannot be the source of natural diamonds.

People also ask

How are diamonds formed?
Diamonds form when carbon is subjected to extreme pressure and high temperature deep within Earth's mantle, typically 150 to 250 kilometers below the surface. The carbon atoms crystallize into a cubic lattice, and the diamonds are later brought to the surface by volcanic eruptions.
What are diamonds made of?
Diamonds are made of pure carbon, the same element found in graphite and all living things. The difference is the arrangement of carbon atoms: in diamond, each carbon atom is bonded to four others in a rigid three-dimensional lattice, while in graphite, the atoms form flat sheets.
Where are diamonds found?
Diamonds are found in rare volcanic pipes called kimberlites, which are mostly located in stable continental regions such as southern Africa, Siberia, Canada, and Australia. They can also be found in secondary deposits, where weathering and rivers have transported diamonds away from their original pipes.
Why are diamonds found only in certain places?
Diamonds are found where ancient volcanic pipes, called kimberlites, have erupted and brought mantle material to the surface. These pipes are rare and mostly located in stable continental regions, so diamond deposits are geographically limited.
Can diamonds form without volcanic eruptions?
Natural diamonds require the high-pressure, high-temperature conditions of Earth's mantle, which are not found at the surface. However, synthetic diamonds can be made in laboratories using chemical vapor deposition or high-pressure presses that mimic mantle conditions.
How long does it take for a diamond to form?
Natural diamond formation takes place over millions to billions of years, as carbon atoms slowly arrange into a crystal lattice under mantle conditions. The ascent to the surface happens quickly, over hours to days, during a volcanic eruption.
What happens to diamonds at Earth's surface?
At the surface, diamond is metastable, meaning it will eventually transform into graphite, the more stable form of carbon. However, this transformation is extremely slow at room temperature, so diamonds can persist for billions of years without noticeable change.

Part of the guide: Nature & Earth: Living Things and Rocks →