Rock Cycle Facts for Children

The rock cycle is a repeating process that causes various types of rocks to form and decay. While the cycles for some types of rocks follow a specific path, not all types of rocks follow the same cycle.

Sedimentary Rocks

Sedimentary rocks are formed from sediments such as sand, silt and clay. Evaporite deposits, such as rock salt and rock gypsum, are types of sedimentary rocks.

Sedimentary Processes

The sedimentary process begins with igneous, sedimentary and metamorphic rocks weathering and eroding. The loose particles then collect in a specific area. Over time, the particles build up, forming layers and compacting the layers of particles resting beneath them. Eventually, the sediments are cemented together by the pressure, forming sedimentary rocks.

Igneous Rocks

Igneous rocks form from the solidification of lava or magma. If it forms intrusively, or within the earth, the rock will have large crystals. Granite is an example of such a coarse-grained igneous rock. If the rock forms extrusively, or on the earth's surface, it will have fine-grained crystals. Obsidian is an example of a fine-grained igneous rock.

Igneous Processes

Igneous, sedimentary and metamorphic rocks are subducted, or pushed down, into the earth where the tectonic plates converge. As a result, the crust melts in the upper mantle and becomes magma. Over time, the magma will either cool and solidify as it rises toward the surface or be ejected from volcanic fissures in an eruption and then cool. Igneous rocks are what is formed by that cooling.

Metamorphic Rocks

Metamorphic rocks are rocks where the crystalline structure of the rock has changed to form a new type of rock. For example, marble is metamorphosed limestone.

Metamorphic Processes

In metamorphism, igneous, sedimentary or other metamorphic rocks are subjected to high temperatures or pressure, which prompts them to recrystallize. The high-pressure exposure could develop from mountain building processes in which two tectonic plates are crashing into each other. The high-temperature exposure could result from a partial subduction of the material that does not lead to melting or from the rock coming in contact with super-heated material seeping through rock fractures. In both cases, the outside forces are not enough to fully melt the rock, but they are enough to recrystallize it.

References

• For Kids: The Rock Cycle
• Instructor Web: The rock cycle