Download Igneous Rocks - Tanque Verde 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
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Igneous Rocks
II. Classification of Igneous Rocks
Igneous rocks can be classified based on
their: texture and composition.
1. Textures
• Coarse-grained texture is caused by slow
cooling resulting in larger crystals.
• Fine-grained texture is caused by rapid
cooling resulting in smaller, microscopic
mineral grains.
Igneous Rocks
Texture (continued)
• Glassy texture is caused by
extremely rapid cooling.
• Porphyritic texture is caused by slow
then rapid cooling. You will see a finegrained texture with larger crystals
within the rock.
• Vesicular – a texture that has lots of
vesicles (holes) from escaping gas.
Course-Grained Igneous Texture
Fine-Grained Igneous Texture
Obsidian Exhibits a Glassy Texture.
Both fine and coarse-grained = porphyritic
Both fine and coarse-grained = porphyritic
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
Classification of Igneous Rocks
TEXTURE DESCRIPTIONS
Classification of Igneous Rocks
WHAT ROCK LOOKS LIKE
Classification of Igneous Rocks
HOW LIGHT OR DARK THE ROCK IS
Classification of Igneous Rocks
NAME OF ROCK
Add these notes to your TOC
• Igneous Rocks Classification
At lab today:
• Look at rock samples– Sketch each rock
– make/ write observations about each
rock in the table
• Such as: texture, composition (colors),
determine type of igneous rock (intrusive,
extrusive); record if there are vesicles, etc
- Name the rock