All rocks on Earth are a part of a large process called the rock cycle. In this cycle, rocks are created and changed by different processes. The graphic representing the rock cycle is intended to show the interrelationships among rocks and the roles of various geologic processes in transforming one rock type into another. This process is called crystalization and can occur above or below the Earth's surface.
Metamorphic rocks are rocks formed by the alteration of preexisting rocks deep within the Earth.
These rocks are altered, but not melted. Sedimentary rocks are rocks formed from unconsolidated materials which were created from weathering and erosion of preexisting rocks.