In class we learned that one type of rock is formed from cooled magma or lava.  If the magma is allowed to cool inside the Earth, then the igneous rock will have big crystals or mineral grains.  This type of igneous rock is called an INTRUSIVE igneous rock.  If the lava reaches the surface is cools RAPIDLY and crystallization happens quickly creating small crystals.  This type of rock is an EXTRUSIVE igneous rock

                                

     left to right: obsidian, granite, scoria (Have you seen these rocks before?)

Sedimentary rocks for over  thousands, even millions of years, little pieces of our earth have been weathered–broken down and worn away by wind and water. These little bits of our earth are carried downstream where they settle to the bottom of the rivers, lakes, and oceans. Layer after layer of eroded earth is deposited on top of each. These layers are pressed down more and more through time, until the bottom layers slowly turn into rock (cementation and compaction)

                               

 left to right: sandstone, conglomerate,  shale (Have you seen these rocks before?)

 

Metamorphic rocks are rocks that have “morphed” or changed into another kind of rock. These rocks were once igneous or sedimentary rocks. How do sedimentary and igneous rocks change? The rocks are under tons and tons of pressure, which fosters heat build up, and this causes them to change.

   

                          left to right: granite, slate, marble (Have you seen these rocks before?)