Diamonds are found in the upper mantle of the Earth, specifically within a region called the lithospheric mantle. This layer is located between about 100 and 200 kilometers (62-124 miles) below the Earth's surface.

Here's a breakdown:

* Mantle: The thickest layer of the Earth, composed of hot, solid rock.

* Lithospheric Mantle: The rigid, outermost part of the mantle, which includes the crust.

* Diamonds: Formed under intense heat and pressure deep within the Earth's mantle.

Diamonds are brought to the surface through volcanic eruptions called kimberlite pipes. Kimberlite is a rare, ultramafic rock that carries diamonds from the mantle to the surface.