1. Chapter 5 “Igneous Rock”

2. Objectives
Describe how the cooling rate of magma & lava affects the texture of igneous rocks.
Classify igneous rocks according to their mineral composition.
Describe a number of identifiable rock structures.

3. 2 types of Igneous Rocks Intrusive Extrusive Created inside the earth
Created on top of the ground

4. Intrusive Igneous Rocks
Magma cools slowly underground
Creates large, well-developed crystals
Example:
Granite

5. Extrusive Igneous Rocks
                     
                      
                      
Extrusive Igneous Rocks
Created when lava cools rapidly
Examples:
Basalt (oceans)
Obsidian (glass)
Pumice (has gas bubbles)

6. What happens if the outside cools rapidly – but the inside cools slowly?
Creates a rock with a porphyritic texture.
Small crystals outside
Quickly formed
Larger crystals embedded inside
Formed slowly

7. Mineral Composition of Igneous Rocks
#1 Felsic
High in silica (SiO)
Examples:
Feldspar, quartz, mica
Granite, Rhyolite, Obsidian
#2  Intermediate
#3  Mafic

8. Mineral Composition of Igneous Rocks (cont.)
#2  Intermediate
Medium colored (grays/browns/reds)
Pink Feldspar
Diorite, Andesite

9. Mineral Composition of Igneous Rocks (cont.)
#3  Mafic
Rich in Magnesium & Iron
Heavy & dense
Olivine, Hornblende
Basalt, Gabbro

10. Igneous Rock Structures
3rd start here wed
Igneous Rock Structures
Intrusions
Formed inside the earth
Extrusions
Formed on the surface

11. Igneous Intrusions Batholiths
Means “deep rock”
Large igneous formations
Must be over 100 km2
The continents are underlain by large batholiths
Similar, smaller areas are called “stocks”

12. Intrusions (cont.) Laccolith Means “layer of rock” Found in groups
Bubbles of magma that have cooled underground
Usually mushroom shaped

13. Intrusions (cont.) Sill Dikes A flat layer of solidified magma
Vertical columns of solidified magma

14. Igneous Extrusions Volcanic Neck What’s left of an ancient volcano
May also include exposed fingers of hardened lava known as dikes

15. Igneous Extrusions (cont.)
Lava flows
Flat layers of solidified lava

16. Igneous Extrusions (cont.)
Lava plateau
Wide, flat areas of hardened lava

17. Assignments:
Complete Chapter 4 interactive notes for Homework

18. Intrusive VS Extrusive
Groups
Felsic
Intermediate
Mafic
Intrusive VS Extrusive