Download Name: : ______ Earth Science Mr. Herman Exeter SHS Chapter 3.2

Name: __________________________________________Date: ___________
Earth Science
Mr. Herman
Exeter SHS
Chapter 3.2 Igneous rocks
Vocabulary
Intrusive igneous rock
Extrusive igneous rock
Porphyritic texture
Granitic composition
Basaltic composition
Andesitic composition
Ultramafic
Objectives
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Compare and contrast intrusive and extrusive igneous rocks.
Demonstrate how the rate of cooling affects an igneous rock’s texture.
Classify igneous rocks according to texture and composition,
Formation of Igneous Rocks
Intrusive igneous rocks are formed when magma hardens beneath Earth’s surface.
Extrusive igneous rocks are formed when lava hardens.
Classification of Igneous Rocks
Igneous rocks can be classified based on their composition and texture.
1. Texture
 Coarse-grained texture is caused by slow cooling resulting in larger
crystals.
 Fine-grained texture is caused by rapid cooling resulting in smaller,
interconnected mineral grains.
 Glassy texture is caused by very rapid cooling
 Porphyritic texture is caused by different rates of cooling resulting in
varied sized minerals.
2. Composition
 Granitic composition rocks are made mostly
of light-colored quartz and feldspar.
 Basaltic composition rocks are made mostly of dark-colored silicate
minerals and plagioclase feldspar.
 Andesitic composition rocks are between granitic light-color minerals
and basaltic composition dark-colored minerals.
 Ultramafic composition rocks are made mostly from iron and
magnesium-rich minerals.