1. The Story of: Igneous Rocks
Section 4-2
Explain how the cooling rate of magma affects the rock texture
Distinguish between Intrusive & Extrusive Igneous rocks

2. Science Starter:
1. Using your notes & section 4.2 in the book, create a T-chart explaining the differences between Intrusive & Extrusive Igneous rocks.
Intrusive Extrusive

3. Igneous Rock Igneous = Latin word for “fire”
Rocks formed from the cooling of magma (or lava).

4. Magma Formation 3 ways magma can form: (p. 98) Rock is HEATed
When PRESSURE is released
When rock changes COMPOSITION

5. Classification of Igneous Rocks:
Composition: what minerals are in the rock
Texture: size of the rocks’ mineral grains(crystals)
Eg. Large grains or small grains

6. Composition of Igneous Rocks:
Composition determines rock color
Dark Colored = Mafic
Made of elements: Calcium, Iron & Magnesium
More Dense
Basalt

7. Composition of Igneous Rocks:
Light Colored = Felsic
Made of elements: aluminum, potassium, silicon
Less Dense
Rhyolite

8. Texture of Igneous Rocks:
How quickly magma cools determines rock texture
Cools slowly= more time for crystals to grow
More time for crystals to grow= larger crystals
Intrusive Igneous Rock
Granite (coarse-grained)

9. Texture of Igneous Rocks:
Cools quickly= little/no time for crystals to grow
no crystals or small crystals
Extrusive Igneous Rock
Obsidian (volcanic glass)

10. Igneous rocks form from molten rock.
4.2
Igneous rocks form from molten rock.
As molten rock cools, minerals crystallize and form Ig. rocks.
intrusive igneous rock
Extrusive igneous rocks cool quickly at Earth's surface.
extrusive igneous rock
Intrusive igneous rocks cool slowly within Earth.

11. Igneous rocks form from molten rock.
4.2
Igneous rocks form from molten rock.
As molten rock cools, minerals crystallize and form Ig. rocks.
intrusive igneous rock
Extrusive igneous rocks cool quickly at Earth's surface.
extrusive igneous rock
Intrusive igneous rocks cool slowly within Earth.

12. Igneous Rock-Intrusive vs. Extrusive
Extrusive Igneous Rock: Cools quickly at Earth’s surface Intrusive Igneous Rock: Cools slowly within Earth
What Texture will Extrusive rocks have?
What Texture will Intrusive rocks have?

13. Magma Formation, cont. Temperature
An increase in temperature from the earth’s interior can cause minerals in rock to melt.
Different minerals have different melting points.

14. Magma formation cont. Pressure:
Earth’s interior=high pressure=rocks stay in their solid form.
As rocks move towards earth’s surface there is less pressure and it sometimes causes them to melt.

15. Magma formation cont. Composition-
Sometimes fluids enter a rock and change its melting point, and ultimately the composition of the rock itself.

16. Igneous Rock Vocabulary:
Composition: Texture:

17. Igneous Rock Vocabulary
Composition: Texture: