Here's why:
* Igneous rocks are formed from the cooling and solidification of magma (molten rock) or lava. Granite specifically forms from the slow cooling of magma deep underground.
* Sedimentary rocks are formed from the accumulation and cementation of sediments like sand, mud, or shells.
* Metamorphic rocks are formed when existing rocks (igneous, sedimentary, or even other metamorphic rocks) are transformed by heat, pressure, or chemical reactions.
So, granite is an igneous rock because it originates from cooled and solidified magma.