ROCKS CHANGE INTO OTHER ROCKS OVER TIME
See “Igneous Rocks” PowerPoint
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.
• 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.