Rocks altered by heat and pressure beneath the surface are called metamorphic rocks.

Here's why:

* Metamorphism is the process of transforming existing rocks (igneous, sedimentary, or even other metamorphic rocks) through intense heat and pressure deep within the Earth's crust.

* Heat can cause minerals to recrystallize, changing their size and arrangement.

* Pressure can cause minerals to become more densely packed, changing the rock's texture.

Examples of metamorphic rocks include:

* Marble: Formed from limestone

* Slate: Formed from shale

* Gneiss: Formed from granite or other igneous rocks

* Quartzite: Formed from sandstone