Here's why:

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

* Pegmatites are specifically formed from very slow-cooling, highly viscous magma, resulting in exceptionally large mineral crystals.

* Sedimentary rocks form from the accumulation and cementation of sediments.

* Metamorphic rocks form when existing rocks are transformed by heat, pressure, or chemical reactions.