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

Here's why:

* Metamorphism: This process involves the transformation of existing rocks (igneous, sedimentary, or even other metamorphic rocks) into new forms due to changes in temperature, pressure, or chemical environment. These changes occur deep within the Earth's crust or upper mantle.

* Heat and Pressure: The intense heat and pressure cause the minerals within the original rock to recrystallize, changing their structure and composition. This results in new mineral assemblages and textures.

Examples of metamorphic rocks:

* Marble: Formed from limestone under heat and pressure.

* Slate: Formed from shale under heat and pressure.

* Gneiss: A banded metamorphic rock formed from igneous or sedimentary rocks under intense heat and pressure.

* Schist: A metamorphic rock with a layered texture, formed from various parent rocks under high heat and pressure.

Let me know if you'd like to learn more about specific types of metamorphic rocks!