Bellwork
November 3rd
Make a venn diagram explaining the similarities
and differences between metamorphic and
igneous rocks.
Igneous Rocks
How Does Igneous Rock Form?
• Form when hot, liquid rock (magma) cools and
hardens
How Does Magma Form?
1. Increase in temperature: when temperature
increases, minerals in rock melt
2. Decrease in pressure: if hot rock rises to the
surface, the pressure goes down, and the
rock will melt
3. Addition of fluids: when fluids mix with rock,
the rock’s melting temperature decreases
and the rock can melt
Check for Understanding
• Give three ways that magma can form.
How Do Igneous Rocks Form, cont.
•
•
•
•
•
When magma cools, mineral crystals form
Similar to ice
Magma = different compounds
Compounds = different minerals
Each mineral becomes solid at different
temperatures
• As magma cools, different parts become solid
at different temperatures
How Do Igneous Rocks Form?
Magma
Cools
Mineral
Crystals
Start To
Form
Magma
Cools
More
Igneous
Rock
Form
Check For Understanding
• Why do different parts of magma become
solid at different times?
How Are Igneous Rocks Classified?
• Composition
• Texture
Composition
– Felsic
•
•
•
•
Rich in Sodium, Potassium, and Aluminum
Combine to make light-colored minerals
Felsic igneous rocks are light-colored
Examples are granite and Rhyolite
– Mafic
•
•
•
•
Rich in Iron, Magnesium, and Calcium
Combine to make dark-colored minerals
Mafic igneous rocks are dark-colored
Examples are gabbro and basalt
Check for Understandin
• Give two differences between felsic and mafic
igneous rocks.
Texture
• Texture of any rock is determined by the sizes
of the grains in the rock
• Texture of an igneous rock depends on how
fast the magma cooled
• Cools fast – small crystals form (fine-grained
texture)
• Cools slow – large crystals form (coarsegrained texture)
Check for Understanding
• Give an example of a felsic, fine-grained
igneous rock.
• Give an example of a mafic, coarse-grained
igneous rock.
Texture: Intrusive Igneous Rocks
• Intrusive Igneous Rocks
– Forms when magma cools below the Earth’s
surface
– Magma cools slowly, so most will have coarsegrained texture
Check for Understanding
• Write your own definition for intrusive
igneous rock.
Texture: Intrusive Igneous Rocks
Volcanic Neck –
forms when a
dike or stock is
exposed to the
surface. The rock
around it erodes
away and only
the igneous rock
is left behind
Stock – large body Batholith –
of intrusive rock
largest kind
of intrusive
rock body
Sill –
sheetlike
body of
intrusive
rock that
is parallel
to other
Dike – rock layers
sheetlike
body of
intrusive rock
that cuts
across other
rock layers
Check for Understanding
• Give four kinds of intrusive rock bodies.
Extrusive Igneous Rocks
• Extrusive Igneous Rocks
– Forms when lava cools
– Common around volcanoes
– Lava cools quickly, so most will have fine-grained
texture
Check for Understanding
• Why do extrusive rocks have very small
crystals or no crystals?