Metamorphic rocks result from the transformation of existing rocks (igneous, sedimentary, or even other metamorphic rocks) due to intense heat and pressure. This process, known as metamorphism, doesn't melt the rock completely like in the formation of igneous rocks. Instead, it changes the mineral composition and texture of the original rock.

Here's a breakdown:

* Heat: This can come from various sources, like the Earth's internal heat, intrusions of magma, or friction from tectonic plate movement.

* Pressure: This can be caused by the weight of overlying rocks, tectonic forces, or the pressure of fluids.

The resulting metamorphic rock is often a stronger, denser, and more resistant rock than the original.

Here are some examples of how different types of rocks are transformed into metamorphic rocks:

* Sedimentary rocks: Limestone turns into marble, sandstone turns into quartzite.

* Igneous rocks: Basalt turns into greenstone, granite turns into gneiss.

* Other metamorphic rocks: Slate can be further metamorphosed into schist.

The specific type of metamorphic rock that forms depends on the original rock type, the intensity of heat and pressure, and the presence of fluids.