​As we have learned there a 3 types of rock: igneous, sedimentary and metamorphic. These different rock types can be transformed into one another. Sedimentary rock can become igneous, metamorphic or another sedimentary rock, metamorphic rock can become igneous, sedimentary or another metamorphic rock and igneous rock can become sedimentary, metamorphic or another igneous rock. The rock cycle describes these changes and how they happen.

These changes occur by processes of:

• weathering and erosion
• melting
• exposure to heat and pressure

Source: http://rockcycle8.wikispaces.com/rock+cycle  

By studying the rock cycle diagram we can see that the rock cycle never ends and by following the arrows the different paths can be seen.