Download - Lesson 1 - Now
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1. Once a rock forms as part of a mountain, it does not change.
2. Some rocks, when exposed on Earth’s surface, undergo weathering and erosion.
Do you agree or disagree?
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• How do igneous rocks form?• What are the common types of
igneous rocks?
Igneous Rocks
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• When volcanic material erupts and cools and crystallizes on Earth’s surface, it forms a type of igneous rock called extrusive rock.
• Volcanic glass is rock that forms when lava cools too quickly to form crystals.
• Among the most noticeable features of some extrusive igneous rocks are holes that are left after gas escapes.
Igneous Rock Formation
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Igneous Rock Formation (cont.)
intrusivefrom Latin intrudere, means “to push in”
Igneous rocks that form as magma cools underground are called intrusive rocks.
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Geologists determine whether an igneous rock is extrusive or intrusive by studying the rock’s texture.
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• If the crystals are small, the rock is extrusive.
• If all the crystals are large enough to see and have an interlocking texture, the rock is intrusive.
Igneous Rock Identification
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• Igneous rocks are also classified, in part, by magma composition, such as silica content.
• Magma composition, the location where the lava or magma cools and crystallizes, and the cooling rate determine the type of igneous rock that forms.
Igneous Rock Identification (cont.)
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Igneous Rock Identification (cont.)
How are extrusive and intrusive rocks different?
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• An extrusive igneous rock cools and crystallizes from volcanic material erupted on Earth’s surface.
• When lava cools fast, volcanic glass forms.
• An intrusive igneous rock forms as magma cools and crystallizes deep inside Earth.
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A. sediment B. volcanic glassC. pumiceD. magma
What erupts onto Earth’s surface during a volcanic eruption?
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A. extrusive rockB. intrusive rockC. volcanic glassD. magma
Which of these forms when lava cools too quickly to form crystals?
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A. intrusive B. extrusiveC. crystallizedD. mineral
What kind of rock forms when magma cools underground?
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3. Large crystals form when lava cools quickly on Earth’s surface.
4. Igneous rocks form when cooling magma crystallizes.
Do you agree or disagree?