Final answer:
Metamorphic rocks are formed by heat, pressure, or chemical reactions acting on igneous and sedimentary rocks. Examples include schist, slate, and marble.
Step-by-step explanation:
Metamorphic rocks are formed by heat, pressure, or chemical reactions within the Earth's crust acting on the other two major types of rocks, which are igneous and sedimentary rocks. The original structure of the rock is altered during metamorphism. Examples of metamorphic rocks include schist, slate, and marble.