1. Igneous Rocks
Rocks Brain-Pop

2. Igneous Rocks
Rocks that form when natural, molten rock-forming material cools and turns into a solid

3. Igneous Rock Formation Video

4. Liquid (molten) rocks Lava – On the Earth’s surface (Extrusive)
Magma – Beneath the Earth’s surface (Intrusive)

5. Cooling Rates Animation
Formation
Solidification – the change from a liquid to a solid
Crystallization – molten magma or lava cools and form solid rocks composed of intergrown mineral crystals
Cooling Rates Animation

6. Intrusive Igneous Rocks:
forms underground
magma never reaches the surface
cools slowly
form large crystals
medium to coarse grained texture
Get exposed at the surface only when rock is uplifted and exposed

7. Intrusive Igneous Rocks Video

8. Extrusive Igneous Rocks:
Forms on the surface
Lava comes out of a volcano
cools rapidly
forms small crystals
glassy or fine-grained
Covers the surface as lava flows or pyroclastic debris

9. Extrusive Igneous Rocks Video

10. CRYSTAL SIZE VS. COOLING TIME
As cooling time increases, crystal size increases.
Crystal
SIZE
Cooling TIME

11. Felsic Mafic Classification of Igneous Rocks:
They are classified according to their chemical composition and texture
Felsic
Rich in:
Silica
Aluminum
Potassium Feldspar
Quartz
Mafic
Rich in:
Iron
Pyroxene
Olivine
The % of different minerals affect the color of the rock
More silica the lighter the rock, less silica the darker
More Iron the darker the rock, less Iron the lighter

12. Classify the following rocks as either: Extrusive or Intrusive Mafic or Felsic
Intrusive + Mafic = Gabbro
Extrusive + Mafic = Basalt
Intrusive + Felsic = Granite
Extrusive + Felsic = Rhyolite

13. Vesicles (Vesicular)
As lava rises and cools to form extrusive igneous rock,
Pressure drops which causes the gases that are in the lava to expand.
These gases form vesicles (cavities) which are the remains of gas bubbles.
Intrusive rocks rarely contain vesicles because they are formed at depth where high pressure stops the gases from expanding.

14. Vesicular Rocks - Pumice

15. Compare Granite and Basalt
Intrusive (large crystals)
Felsic (Light In Color)
Basalt -
Extrusive (Small Crystals)
Mafic (Dark In Color)

17. Crystal Size Animation
Crystallization:
Magma is a mixture of different substances. They all have different melting points.
So as magma cools, some substances will form crystals before other substances. They have a head start in growth and tend to be bigger.
If the magma already has crystals present in it and then is cooled rapidly then you will see large crystals embedded in finer-grained material.
This is called a porphyritic texture

21. Basaltic lava in Hawaii
Top: Basaltic lava flow
Bottom: Slow moving lava

22. Magma & Lava Video

23. Mt. St. Helens
Pre eruption
Post eruption
(May 1980)

24. Vocabulary: magma, lava, intrusive, extrusive, vesicles, felsic, mafic
Igneous Rock Review
1. What is the difference between magma and lava?
2. What are the two main types of igneous rocks?
3. How can you tell them apart?
4. Why is it not common for Intrusive rocks to have vesicles?
Vocabulary: magma, lava, intrusive, extrusive, vesicles, felsic, mafic