What kinds of rocks can undergo metamorphism?

The processes that transform one type of rock into another are collectively referred to as metamorphism. Metamorphic rock is one of the three main types of rocks; the other two are igneous and sedimentary.

When it comes to metamorphism, the original rock type doesn't really matter because any rock can go through it if it is heated and/or buried deeply enough. A rock's constituent minerals change to become more chemically stable when the pressure and temperature acting on it change.

For example, eclogite, a metamorphic rock, can be formed from basalt, an igneous rock, by subjecting it to extremely high pressure and moderate temperature. This is because the minerals within the basalt undergo transformation into other minerals that are more stable under extreme conditions. Nevertheless, eclogite is still capable of metamorphism; this occurs when a body of eclogite is uplifted and the pressure upon it decreases, converting it into a new rock known as granulite.

Any type of rock, including sedimentary, igneous, or even pre-existing metamorphic rocks, can undergo metamorphism under the right conditions of temperature, pressure, and chemical environment.