Earth and Space > The Rock Cycle
The Rock Cycle describes the transitions between sedimentary, metamorphic and igneous rock types over time. Over many years, each type of rock can change its appearance and characteristics when it is subjected to different environments such as weathering, heat and or great pressure. The diagram below shows the ways in which one type may change into another through these environmental factors.
Fig 1: The rock cycle
When rocks are open to the elements they can become weathered and eroded fragmenting them into smaller parts. These parts may settle down over time, and accumulate for example on a sea bed. Over time, these fragments may fuse together becoming sedimentary rock. Examples of sedimentary rocks are: Sandstone, shale, limestone.
When rocks are pushed under the earth’s surface through plate movements, they melt into magma. When this magma cools into a solid state, it turns into an igneous rock. Magma that is cooled very slowly within the earth is called an intrusive igneous rock, whereas magma that is cooled rapidly, such as the magma expelled from volcanoes is labelled extrusive. Igneous rocks include: Basalt, Obsidian, Rhyolite.
Rocks under extreme pressure and heating can be physically or chemically changed into metamorphic rocks. These rocks sometimes have bands of coloured minerals running through them. Examples include: Slate, Marble, Gneiss, Quartzite.