Here's why:

* Intrusive rocks form when magma cools and solidifies beneath the Earth's surface. Kimberlite forms deep within the mantle and is brought to the surface by powerful volcanic eruptions.

* Extrusive rocks form when lava cools and solidifies on the Earth's surface. While kimberlite is associated with volcanic activity, it itself doesn't typically solidify on the surface.

The eruption of kimberlite magma creates characteristic pipe-shaped structures, often referred to as "kimberlite pipes" or "diatremes." These pipes are the primary source of diamonds, which are formed under extreme pressure deep within the Earth.