The type of rock that forms when extreme heat and pressure are applied is metamorphic rock.

Here's why:

* Metamorphism is the process of changing existing rocks (igneous, sedimentary, or even other metamorphic rocks) into new rocks through intense heat and pressure.

* This process doesn't melt the rock completely (like in magma formation), but it does transform the rock's mineral composition, texture, and sometimes even its chemical composition.

Let me know if you want to know more about the different types of metamorphic rocks!