How natural diamonds form
Carbon, heat, pressure and a very long time.
By the CTJ Jewellery team, led by founder Greg Ward · Updated September 2026 · Editorial policy
Key facts
- Depth: about 150 to 200 km
- Temperature: roughly 900 to 1,300°C
- Age: typically 1 to 3.5 billion years
- Carried up in kimberlite and lamproite pipes
- Also found in riverbeds and coastal deposits
- Australia’s Argyle mine in WA closed in 2020
Where do natural diamonds come from?
They come from the mantle, far below the earth’s crust, where carbon is stable as diamond. Only a small share of the rock brought up by eruptions contains diamonds, and fewer still are gem quality.
How do diamonds reach the surface?
Rare, very deep eruptions rose quickly enough to carry diamonds up without turning them to graphite. They cooled into carrot-shaped columns of rock called kimberlite pipes. Erosion also washed some diamonds into rivers and onto coastlines.
Why do natural diamonds have inclusions?
As a crystal grew, tiny minerals and structural features were trapped inside. These inclusions are a record of each diamond’s formation and are graded under clarity.
Clarity explainedHow is this different from a lab-grown diamond?
A lab-grown diamond recreates similar conditions (HPHT) or builds carbon from a gas (CVD) over weeks. The result is the same material, so only laboratory equipment can tell them apart.
Natural and lab-grown compared