The Rock Cycle
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The continual process by which new rock forms from old rock material is called the rock cycle. The rock cycle can change an Igneous Rock into a Sedimentary Rock, Metamorphic Rock or even back to Igneous Rock. There are three main types of rocks: igneous, sedimentary, and metamorphic. All Igneous rocks start out as melted rock (magma) and then crystallize or freeze. Metamorphic rocks form when sedimentary, igneous, or other metamorphic rocks are subjected to heat and pressure from burial or contact with intrusive or extrusive igneous rocks. Sedimentary rocks are made up of smaller rocks. Rocks might go on different pathways in the rock cycle. As one rock type is changed into another, several variables incorporating heat, pressure, time, weathering and erosion may change the identity of the rock. Rocks at the Earth's surface are mainly changed by weathering and erosion, but deep inside the Earth, rocks change from major heat and pressure. If a metamorphic rock were to change into an Igneous rock, it would first melt into magma, then it would cool into an igneous rock. James Hutton, a geologist developed the first version of the rock cycle in the 1700's. Since then, geologist have changed the rock cycle to include new information. (Information from: Imnh.isu.edu.com, www.mrjandrews.wikispace.com, www.wisegeek.com, Holt Science and Technology Textbook.)