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.

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.