Rock Cycle

The last cycle we will discuss is the rock cycle. This involves the recognition of three main classes of rocks found on the Earth.

 
• Igneous: These rocks, such as basalt and granite, are formed from when magma or lava from volcanoes hardens. These were the first types of rock to appear on the Earth.  
• Sedimentary: These rocks, such as sandstone, shale, and limestone, are formed from the erosion of other types of rocks by weather and water.  
• Metamorphic: When sedimentary rocks get buried deep within the Earth, they are subject to intense pressure and heat. This changes the rock into a metamorphic rock, examples of which are quartzite.

The rock cycle consists of the production and transformation of one type of rock into another: lava hardens to form an igneous rock, which subsequently is eroded into a sedimentary rock, which in turn can transform into a metamorphic rock.