Do you know what the rock cycle is? Besides a cycle about rocks, obviously. The rock cycle is how rocks change into one another. Take a look at the diagram below:
Igneous rock forms from cooled magma which makes crystals. Several things could happen to this igneous rock- It could, after adding heat and pressure, become metamorphic rock; it could weather down into tiny pieces of rock called sediment, which is then compacted to become sedimentary rock; or it could melt back into magma that might cool and become igneous rock again.
Now, say the igneous rock became metamorphic rock when heat and pressure was added. The heat and pressure from inside Earth bakes the rock; instead of a cake like when you bake, though, crystals form, or, if there were already crystals, larger crystals are formed. Since the rock changes, it is called metamorphic rock, as in metamorphosis- when a caterpillar changes into a butterfly. The metamorphic rock is still made of what igneous rocks are made of, so it could also melt into magma. Or, again like the igneous rock, it could be weathered down into sediments.
All the rocks can be weathered into sediment, actually. Especially sedimentary rock, which is made of sediments. To form sedimentary rock, layer after layer of sediment is laid down, eventually cementing into sedimentary rock; this is why sedimentary rock has layers. If you were to add heat and pressure to that sedimentary rock, it would become metamorphic rock.
As you can see, all the rocks are connected, changing into each other again and again. That is why, after all, they call it a rock cycle.
Source:
http://www.cotf.edu/ete/modules/msese/earthsysflr/rock.html
Now, say the igneous rock became metamorphic rock when heat and pressure was added. The heat and pressure from inside Earth bakes the rock; instead of a cake like when you bake, though, crystals form, or, if there were already crystals, larger crystals are formed. Since the rock changes, it is called metamorphic rock, as in metamorphosis- when a caterpillar changes into a butterfly. The metamorphic rock is still made of what igneous rocks are made of, so it could also melt into magma. Or, again like the igneous rock, it could be weathered down into sediments.
All the rocks can be weathered into sediment, actually. Especially sedimentary rock, which is made of sediments. To form sedimentary rock, layer after layer of sediment is laid down, eventually cementing into sedimentary rock; this is why sedimentary rock has layers. If you were to add heat and pressure to that sedimentary rock, it would become metamorphic rock.
As you can see, all the rocks are connected, changing into each other again and again. That is why, after all, they call it a rock cycle.
Source:
http://www.cotf.edu/ete/modules/msese/earthsysflr/rock.html