1. Chapter 6 - 2
Igneous rocks

2. Igneous Rock
When magma cools and hardens
Most made of crystals

3. Magma Formation 3 factors: 1. Temperature 2. Pressure 3. Fluid in rock
Melting point determined by chemical composition

4. Melting
Water added to hot rock causes melting
Decreases melting point

5. Partial Melting
Partial melting – different minerals in rock melt at different temperatures

6. Fractional Crystallization
Chemicals in magma combine to form minerals
Each have different freezing points
F.C. – crystallization and removal of different minerals during cooling

7. Crystals
Crystals that form early are larger
More time to form

8. Intrusive Igneous Rocks
Formed from magma cooling inside the Earth
More time to cool
Larger crystals

9. Extrusive Igneous Rocks
Formed from lava cooling outside of the crust
Cools faster
Less time for crystals to form - smaller

10. Coarse-Grained Igneous Rocks
Large mineral grains
Cooled slowly
Intrusive
Granite

11. Fine-Grained Igneous Rocks
Small mineral grains
Very hard to see
Cooled fast
Extrusive
Basalt

12. Other Textures Porphyritic texture – large and small crystals
Formation?
Glassy Texture – cooled fast with low dissolved gases

13. Vesicular texture – lots of gases trapped
Fast cooling
Vesicles – holes in rock

14. 3 Families
3 Families determined by mineral composition

15. Felsic Contains a lot of silica Light colored Granite Rhyolite
Obsidian
Pumice

16. Mafic Lower amounts of silica Irion and magnesium Darker coloring
Basalt
Gabbro

17. Intermediate
Intermediate amounts of silica
Diorite
Andesite

18. Batholiths Large igneous intrusion At least 100km2 when exposed
“Deep rock”
1,000’s of meters deep

19. Stocks
Cover less than 100 km2
Small intrusion

20. Laccoliths Magma flows between rock layers Pushed rock into a dome
“Lake of rock”

21. Sills Magma flows between rock layers and hardens
Centimeters to 100’s of meters
Parallel to rock layers

22. Dikes
Magma forces through cracks and hardens
Cut across rock layers

23. Igneous Extrusions Form on Earth’s surface
Volcano – vent for magma and gases
Volcanic neck – soft parts of volcano erode away

24. Lava Flows
Lava flows – flat masses of rock

25. Lava Plateau
Lava flow that covers a large area of land

26. Tuff
Tuff – ash and other solid particles released from a volcano