* Igneous rocks form from the cooling and solidification of magma or lava. This means the rock must first be melted.

* Roches sédimentaires are formed from the accumulation and cementation of sediments (like sand, mud, or shells). They don't melt easily.

* Rocks métamorphiques are formed when existing rocks (igneous, sedimentary, or other metamorphic rocks) are transformed by heat and pressure. While metamorphic rocks can melt to form magma, this isn't a direct transformation.

Here's how igneous rocks can form from other types of rocks:

* Magma can be generated from melting sedimentary rocks: This usually occurs deep underground when sedimentary rocks are buried and subjected to high temperatures and pressures.

* Magma can be generated from melting metamorphic rocks: This happens when metamorphic rocks are brought to the surface and undergo partial melting.

* Igneous rocks can be re-melted to form new igneous rocks: This process is called "recycling" and is common in certain geological settings.

So, while igneous rocks can form from other rock types, it's not a direct process. It always involves melting and then cooling and solidifying.