Here's why:

* Igneous: Pyrite forms during the cooling and solidification of magma or lava. It can be found in both intrusive and extrusive igneous rocks.

* Metamorphic: Pyrite can also form during the transformation of existing rocks under heat and pressure. It's commonly found in metamorphic rocks like schists and slates.

* Sedimentary: While pyrite can be found in sedimentary rocks, it's less common. It usually forms during the diagenetic processes (changes after deposition) or from the weathering of igneous or metamorphic rocks containing pyrite.

So, while you can find pyrite in all three rock types, it's more typical of igneous and metamorphic formations.