1. Chapter 4 Sections 1 and 2 Rock Cycle and Igneous Rocks

2. What is a rock?
A rock is a mixture of broken rock fragments, volcanic glass, organic matter, and other natural materials.
Example of
Andesite

3. Common Rock Forming Minerals
Quartz
Feldspar
Hornblende
Mica
Example of
granite

4. The Rock Cycle
crystallization

5. The Rock Cycle
The rock cycle shows how rocks slowly change through time.
The rock cycle shows the three types of rocks-igneous, metamorphic, and sedimentary and the processes that form them.
Example: A sedimentary rock can change by heat and pressure to form a metamorphic rock. The metamorphic rock can melt and cool to form and igneous rock. The igneous rock can be broken into sediments by weathering and eroding away. The sediments might then compact and cement together to form a sedimentary rock.

6. Example of Metamorphic Rock Gneiss

7. Example of Sedimentary Rock Conglomerate

8. Example of an Igneous Rock

9. Rock Cycle The main processes found in the rock cycle are
Melting and Cooling magma form igneous rocks.
Weathering and erosion break rocks into sediments.
Compaction and Cementation change rocks into sedimentary rocks.
Heat and Pressure form metamorphic rocks

11. Formation of Igneous Rocks
When hot magma cools and hardens, it forms igneous rocks.
Because magma is less dense than surrounding rocks, it is forced upward towards the surface. When magma reaches the Earth’s surface and flows from volcanoes it is called lava.

12. Lava Picture before solidification

13. Lava picture after solidification

14. Intrusive rocks
Rocks that form from magma below the surface of Earth are called intrusive igneous rocks. (intrusive=inside).
Intrusive igneous rocks take a long time to form. Slowly cooled magma produces large individual mineral grains in the rocks.

15. Granite

16. Diorite

17. Gabbro

18. Extrusive Rocks
Extrusive igneous rocks are formed as lava cools on the surface of the Earth. (extrusive=exterior=outside).
When lava flows on the surface it is exposed to air and water. Under these conditions the lava cools very quickly.
When the lava cools quickly, the atoms in the liquid don’t have time to arrange into large crystals, which is why extrusive igneous rocks are fine-grained.

19. Extrusive Rocks
Pumice and Obsidian are examples of volcanic glass. These rocks cooled so quickly that few or no mineral grains formed.
In the case of pumice gases became trapped in the molten material as it cools. The gases escape, but holes are left behind where the rock formed around the pockets of gas.

20. Basalt

21. Rhyolite

22. Andesite

23. Pumice

24. Obsidian

25. Classifying Igneous Rocks
Igneous rocks are intrusive or extrusive depending on how they formed.
A further way is to classify these rocks is by the magma from which they formed.
Basaltic igneous rocks are dense, dark-colored rocks. They form from magma that is lacking silicon.
-Basaltic lava is fluid and flows freely from volcanoes in Hawaii.
-These rocks are also called mafic igneous rocks.
-These rocks compose the seafloor.

26. Classifying Igneous Rocks
Grantic igneous rocks are light-colored rocks of lower density than basaltic rocks. Granitic magma is think and stiff and contains a lot of silica.
Grantic magma is stiff and builds up a a large amount of gas pressure which is released explosively during a volcanic eruption.
These rocks are called felsic igneous rocks.
The continents are composed mainly of granite.

27. Classifying Igneous Rocks.
Andestic igneous rocks have mineral compositions between those of granitic and basaltic rocks. Many volcanoes around the rim of fire formed from andesitic magma.