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Monday, January 28, 2013

The Rock Cycle

     Rocks form in a cycle.  There are a series of events that move a rock around the cycle.  Those events can make a rock igneous, sedimentary, or metamorphic depending on what events occurred and where.
     There are many things that occur to change a rock from one kind to another.  In order for a rock to be sedimentary it has to weather and erode then later compact and cement together into a rock.  In order for an igneous rock to form, another rock has to melt and then cool.  In order for a rock or rocks to become metamorphic they have to layer underground then heat and pressure squeezes them together into a rock.
     Igneous rocks start to form underground where rocks and minerals melt into magma.  Later the magma shoots up out of the ground and pushes the earth up with it.  It bursts through the earth and becomes lava.  The lava cools and becomes igneous rock.  Some of the magma doesn't become lava, but forms pockets underground.  The magma that is in the pockets cools into intrusive igneous rock.  The lava that cools above ground becomes extrusive igneous rock.  Like igneous rock metamorphic rock one of the processes is heat.
       Metamorphic rock forms in layers underground.  The layers heat up and press together.  They press together into metamorphic rock.  Sedimentary rock is weathered or eroded into sediments then deposited into a river, lake, or stream.  Then the sediments are cemented together under the weight of the water.
     This is the rock cycle.  Rocks change over time.  Heat, pressure, weathering and erosion, compaction and cementation, and cooling help change rocks from rock type to rock type.