Igneous Rock: How does the cycle begin? The rock cycle is usually said to begin with a hot molten liquid rock called magma or lava. Magma forms under the Earth’s surface in the crust or mantle and erupts on Earth’s surface as lava. We are all familiar with volcanoes, and it is out of these volcanoes that lava can flow. When magma or lava cools, it solidifies by crystallization, in which minerals grow within the magma or lava. The rock that results from this is called igneous rock from the Latin word ignis, meaning “fire.”

Sedimentary Rock: All rocks on the earth's surface are exposed to the weather. Weathering is the physical and chemical breakdown of rocks into smaller fragments. Once rocks have been broken up by weathering, they are transported by water in streams, ice in the form of glaciers, and air in the form of wind. Small particles of rock, (sediment) eventually come to rest in a place, often underwater such as a shallow marine environment, and in turn get buried by more sediment. Layers of various sediments build up and are compacted and cemented into a semi-hard stone.

Metamorphic Rock: Either igneous or sedimentary rocks can be changed into a different form of rock through extreme pressure and temperature. These temperatures and pressures occur when rocks are buried deep within the earth's crust, or encounter hot magma or lava. Certain metamorphic rocks such as marble or coal are formed from living creatures that have been deeply buried and subjected to great pressure and temperature.