1. Igneous Rocks

2. Anticipation guide #3
1) Igneous rocks were the first rocks created on Earth
2) Basalt is a rock that makes up the continents
3) Rocks can be classified by mineralogy, texture and process
4) The size of the crystals in rocks depends on the solidification rate
5) Granite is an extrusive rock

3. VA SOL
SOL 5 The student will investigate and understand common rock types based on mineral composition and textures and the rock cycle as it relates to the origin and transformation of rock types. Key concepts include
a. igneous (intrusive and extrusive) rocks;

4. Objective Classify igneous rocks by mineral content and texture.
Intrusive – granite;
Extrusive – pumice, obsidian, and basalt.

5. Enduring Understanding
The rock cycle is an ongoing process by which rocks are formed. It gives us an explanation of how Earth materials are recycled through time.
Virginia has many natural resources.

6. Igneous Rocks
Minerals combine in the Earth’s crust to form rocks. Most rocks are made of one or more minerals. Igneous rocks were the first type to form on Earth as its molten surface cooled and solidified

7. Igneous Rocks
Igneous Rocks form from the crystallization of magma

8. Igneous Rocks
Magma is molten rock below Earth’s surface

9. Igneous Rocks
Lava is magma that flows out onto Earth’s surface

10. Igneous Rock Types
Igneous rocks are classified based upon where they form
Extrusive igneous rocks cool quickly on the surface and are fine-grained (small crystals)

11. Igneous Rock Types
Rhyolite is the most common extrusive igneous rock

12. Igneous Rock Types
Other common extrusive igneous rocks include pumice, obsidian, and basalt
Pumice
Obsidian
Basalt

13. Igneous Rock Types
Intrusive igneous rocks cool slowly beneath the surface and are coarse-grained (larger crystals)

14. Igneous Rock Types
Granite is the most common intrusive igneous rock

15. Magma
Magma is often a slushy mix of molten rock, gases and mineral crystals.
The elements in magma are the same major elements found in the Earth’s crust: oxygen (O), silicon (Si), aluminum (Al), iron (Fe), magnesium (Mg), calcium (Ca), potassium (K), and sodium (Na)

16. Magma
Silica (SiO2) is the most common compound in magma and has the greatest effect on its characteristics
Rhyolitic magma has an SiO2 content of 70%
Andesitic magma has an SiO2 content of 60%
Basaltic magma has an SiO2 content of 50%

17. Magma Formation
There are four main factors that affect magma formation
Temperature. Heat comes from the remaining energy from Earth’s formation and the decay of radioactive elements

18. Magma Formation
Pressure. The pressure increases with depth

19. Magma Formation
Water content. More decreases the melting point of the rocks

20. Magma Formation
Mineral content. Minerals melt at different temperatures

21. Classifying Igneous Rocks
Extrusive and intrusive igneous rocks are further classified by their mineral compositions

22. Classifying Igneous Rocks
Felsic rocks are light colored, have high silica contents, and contain quartz and the feldspars orthoclase and plagioclase
Granite is the most common felsic rock

23. Classifying Igneous Rocks
Intermediate rocks are darker than felsic and have moderate amounts of biotite, amphibole, and pyroxene
Diorite is a good example of an intermediate rock

24. Classifying Igneous Rocks
Mafic rocks are dark, have lower silica contents and are rich in iron and magnesium
Basalt is a mafic rock

25. Classifying Igneous Rocks
Ultramafic rocks have low silica contents and very high levels of iron and magnesium.
Olivine is an ultramafic rock

26. Bowen’s Reaction Series
As magma cools, minerals form in predictable patterns. The reaction series has two main branches of crystallization

27. Bowens Reaction Series

28. Bowen’s Reaction Series
Feldspars undergo a continuous change in composition. The first to form are rich in calcium and as cooling continues the feldspars react with the magma and change to sodium rich
Iron-rich minerals undergo abrupt changes during fractional crystallization

29. Bowens Reaction Series

30. Bowen’s Reaction Series
As minerals form in the order shown in Bowens reaction series, elements are removed from the remaining magma. Silica and Oxygen are the most abundant elements and are left over at the end of the reaction series. The remaining magma finally crystallizes to form quartz.

31. Bowens Reaction Series