Download Igneous Rocks - Tanque Verde Unified School District

Igneous Rocks
Igneous Rocks
I. Formation of Igneous Rocks
1. Intrusive igneous rocks are formed when
magma hardens beneath Earth’s surface.
• Obvious crystals/mineral grains.
• Takes a long time to form.
2. Extrusive igneous rocks are formed when
lava hardens above Earth’s surface.
• No obvious crystals.
• Takes a relatively short amount of time.
http://www.classzone.com/books/earth_science/terc/content/investigations/es0603/es0603page05.cfm?chapter_no
=investigation
Igneous Rocks
II. Classification of Igneous Rocks
Igneous rocks can be classified based on
their composition and texture.
1. Texture… (3 kinds of texture)
• Coarse-grained texture is caused by slow
cooling resulting in larger crystals.
• Fine-grained texture is caused by rapid
cooling resulting in smaller, often
microscopic mineral grains.
Igneous Rocks
Texture (continued)
• Glassy texture is caused by extremely
rapid cooling.
Course-Grained Igneous Texture
Fine-Grained Igneous Texture
Obsidian Exhibits a Glassy Texture.
Igneous Rocks
2. Composition - What the rock is
made of
• Granitic composition rocks are made
mostly of light-colored minerals like
quartz and feldspar.
• Basaltic composition rocks are made
mostly of dark-colored silicate minerals
like pyroxene.
Igneous Rocks
b. Composition (continued)
• Andesitic composition rocks are
between granitic light-color minerals
and basaltic composition dark-colored
minerals.
• Ultramafic composition rocks are made
mostly from dark and heavy minerals
like olivine.
Classification of Igneous Rocks
Assignment
• Look at 4 rock samples– Sketch and make/ write observations
about each on your notes page
• Such as: texture, composition (colors),
determine type of igneous rock (intrusive,
extrusive); record if there are pores, etc