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Igneous rocks form from molten rock.

     Magma and lava form different types of igneous rocks.

     Igneous rocks form from molten rock that has cooled. 

     Molten rock comes from deep within the Earth. 

     There temperatures are hot enough to melt rock: 14000-23000 F.

     Magma vs. lava


Classifying igneous rocks

     Based on two factors:                      

1)  mineral composition           

 2)  size of crystals

     Rocks with larger mineral crystals are more attractive.


Intrusive and extrusive igneous rocks

1) intrusive igneous rock-   rock that forms when magma cools within the Earth.

2) extrusive igneous rock-  rock that forms when lava cools at the Earth’s surface.


Extrusive igneous rocks

     Igneous rocks make long lasting landforms.

     Ship Rock (New Mexico)

     A great peak that rises out of the flat, barren desert.

     Great example of a natural feature on the Earth’s surface (landform) that is made of igneous rocks.


Extrusive formations

     The Hawaiian Islands are built of basalt lava.

     Basalt lava flows long distances.

     The volcanoes that formed them started erupting on the sea floor and over a very long time they grew tall enough to rise out of the ocean!

     Mt. Saint Helens (Washington)

     This volcano’s lava is silica rich.

     This lava builds cone shaped volcanoes with steep sides. 

     These erupt explosively since the lava is thick, sticky and under high pressure.