Diamonds are formed deep within the Earth's mantle, specifically at depths of 100 to 200 miles (160 to 320 kilometers). This is a region of intense heat and pressure, where the carbon atoms that make up diamonds are subjected to extreme conditions.

Here's a breakdown:

* Deep within the Earth's mantle: This is the layer beneath the Earth's crust, extending down to about 1,800 miles (2,900 kilometers).

* Intense heat and pressure: The extreme temperatures and pressures within the mantle force carbon atoms to bond together in a highly organized crystal structure.

* Crystallization: Over millions of years, these carbon atoms crystallize, forming diamonds.

It's important to note that diamonds are not formed everywhere within the mantle. They form in specific regions where the right combination of heat, pressure, and carbon content exists.

These diamonds are eventually brought to the surface through volcanic eruptions, carried by magma that rises to the Earth's crust. That's how diamonds end up in kimberlite pipes, which are volcanic conduits that have brought diamonds up from deep within the Earth.