The original rock that undergoes metamorphic changes is called the parent rock or protolith.

It can be any type of rock:

* Igneous rocks: These are formed from the cooling and solidification of magma or lava. Examples include granite, basalt, and gabbro.

* Sedimentary rocks: These are formed from the accumulation and cementation of sediments. Examples include sandstone, limestone, and shale.

* Other metamorphic rocks: Yes, even existing metamorphic rocks can be further metamorphosed, leading to a new metamorphic rock type.

The specific type of parent rock will determine the resulting metamorphic rock. For example, limestone will metamorphose into marble, while sandstone will metamorphose into quartzite.

Let me know if you'd like to know more about the types of metamorphic rocks or the processes involved in metamorphism!