* Igneous rocks form from the cooling and solidification of molten rock (magma or lava).

* Metamorphic rocks form when existing rocks (igneous, sedimentary, or even other metamorphic rocks) are transformed by heat, pressure, or chemically active fluids.

Diamonds are formed deep within the Earth's mantle under immense pressure and high temperatures. The original material is usually carbon-rich minerals like graphite. These conditions cause the carbon atoms to rearrange into the tightly packed, crystalline structure that defines diamond.

So, while diamonds originate from the Earth's interior (like igneous rocks), they are created through the metamorphic process of transformation.