1. Rocks
3.1 The Rock Cycle
 Rocks are any solid mass of minerals, or mineral-like matter, occurring naturally as part of our planet.
 Types of Rocks
1. Igneous rock is formed by the crystallization (hardening) of molten magma.

2. 3.1 The Rock Cycle Rocks  Types of Rocks
2. Sedimentary rock is formed from the weathered products of preexisting rocks that have been transported, deposited, compacted, and cemented.
3. Metamorphic rock is formed by the alteration (change) of preexisting rock deep within Earth (but still in a solid state) by heat, pressure, and/or chemically active fluids.

3. 3.1 The Rock Cycle The Rock Cycle
 Shows the relationships between the three rock types (igneous, sedimentary, metamorphic)
 Magma is molten (melted) material that forms deep beneath the Earth’s surface.
 Lava is magma that reaches the surface.
 Weathering is a process in which rocks are broken down by water, air, and living things.
 Sediment is weathered pieces of Earth elements.

4. 3.1 The Rock Cycle

5. 3.1 The Rock Cycle The Rock Cycle
Magma forms when rock melts deep beneath Earth’s surface.
When magma or lava cools and hardens, igneous rocks form.
Rocks at Earth’s surface are broken down into smaller pieces called sediments.
When sediments are compacted and cemented, sedimentary rocks form.
Any type of rock that is changed by heat, pressure or chemicals becomes metamorphic.

6. 3.1 The Rock Cycle Energy That Drives the Rock Cycle
 Processes driven by heat from the Earth’s interior are responsible for forming both igneous rock and metamorphic rock.
 Weathering and the movement of weathered materials are external processes powered by energy from the sun.
 External processes produce sedimentary rocks.

7. REVIEW
*Remember igneous rocks form when magma or lava cools and hardens. Different kinds of igneous rocks form when magma and lava cool and harden.

8. 3.2 Igneous Rocks Formation of Igneous Rocks
1. Intrusive igneous rocks are formed when magma hardens beneath Earth’s surface.
2. Extrusive igneous rocks are formed when lava hardens above Earth’s surface.

9. 3.2 Igneous Rocks Classification of Igneous Rocks
 Igneous rocks can be classified based on their composition and texture.
1. Texture
• Coarse-grained texture is caused by slow cooling resulting in larger crystals.
• Fine-grained texture is caused by rapid cooling resulting in smaller, connected mineral grains.

10. Coarse-Grained Igneous Texture
Granite is an intrusive igneous rock that forms when magma cools slowly beneath Earth’s surface.

11. Fine-Grained Igneous Texture
Rhyolite is an extrusive igneous rock that forms when lava cools quickly at Earth’s surface.

12. 3.2 Igneous Rocks Classification of Igneous Rocks
1. Texture (continued)
• Glassy texture is caused by very rapid cooling.
• Porphyritic texture is caused by different rates of cooling resulting in varied sized minerals.
2. Composition
• Granitic composition rocks are made mostly of light-colored quartz and feldspar.

13. Obsidian Exhibits a Glassy Texture.
Obsidian is an extrusive igneous rock.

14. Porphyritic Igneous Texture
Andesite displays igneous rock with a porphyritic texture. How did this rock probably form?

15. 3.2 Igneous Rocks Classification of Igneous Rocks
2. Composition (continued)
• Basaltic composition rocks are made mostly of dark-colored silicate minerals and feldspar.
• Andesitic composition rocks are between granitic light-color minerals and basaltic composition dark-colored minerals.
• Ultramafic composition rocks are made mostly from iron and magnesium-rich minerals.

16. Basalt
Basalt is an igneous rock made mostly of dark colored silicate minerals.

17. Classification of Igneous Rocks

18. REVIEW
Igneous rocks are classified based on their texture and composition.

19. 3.3 Sedimentary Rocks Formation of Sedimentary Rocks
 Weathering, Erosion, and Deposition
• Erosion involves the weathering and the removal of rock.
• Deposition occurs when an agent of erosion—water, wind, ice, or gravity—loses energy and drops sediments.

20. 3.3 Sedimentary Rocks Formation of Sedimentary Rocks
 Compaction and Cementation
• Compaction is a process that squeezes, or compacts, sediments.
• Cementation takes place when dissolved minerals are deposited in the tiny spaces among the sediments.

21. 3.3 Sedimentary Rocks Classification of Sedimentary Rocks
 Two Main Groups
1. Clastic sedimentary rocks are composed of weathered bits of rocks and minerals.
• Classified by particle size
• Common rocks include
- Shale (most abundant)
- Sandstone
- Conglomerate

22. Shale with Plant Fossils

23. Conglomerate
Conglomerate is made of rounded pebbles cemented together.

24. 3.3 Sedimentary Rocks Classification of Sedimentary Rocks
 Two Main Groups
2. Chemical sedimentary rocks form when dissolved substances precipitate, or separate, from water.
Common rocks include
- limestone—most abundant chemical rock
- microcrystalline quartz known as chert, flint, jasper, or agate
- evaporites such as rock salt or gypsum
- coal

25. Fossiliferous Limestone
This biochemical rock, called coquina, is a type of limestone that is made of hundreds of shell fragments.

26. Classification of Sedimentary Rocks

27. 3.3 Sedimentary Rocks Features of Some Sedimentary Rocks
Features of sedimentary rocks are clues to how and where the rocks are formed
In undisturbed rocks, the oldest layers are found at the bottom.
Ripple marks indicate that the rock may have formed along a beach or stream.
Mud cracks can indicate the rock formed in a dry environment.

28. 3.4 Metamorphic Rocks Formation of Metamorphic Rocks
 Metamorphism means “to change form.”
 Most metamorphic changes occur at elevated temperatures and pressures.
 Conditions for formation are found a few kilometers below the Earth’s surface and extend into the upper mantle.

29. 3.4 Metamorphic Rocks Formation of Metamorphic Rocks
 Contact metamorphism occurs when magma moves into rock.
Occurs near a body of magma
Changes are driven by a rise in temperature.

30. 3.4 Metamorphic Rocks Formation of Metamorphic Rocks
 Regional metamorphism results in large-scale deformation and high-grade metamorphism.
Directed pressures and high temperatures occur during mountain building.
Produces the greatest volume of metamorphic rock

31. 3.4 Metamorphic Rocks Agents of Metamorphism  Heat  Pressure
Provides the energy needed to drive chemical reactions
 Pressure
Causes a more compact rock with greater density

32. 3.4 Metamorphic Rocks Agents of Metamorphism  Hydrothermal Solutions
Hot water-based solutions escaping from the mass of magma
Promote recrystallization by dissolving original minerals and then depositing new ones

33. 3.4 Metamorphic Rocks Classification of Metamorphic Rocks
 Two main categories
1. Foliated Metamorphic Rock
Has a banded or layered appearance
2. Nonfoliated Metamorphic Rock
Does not have a banded texture

34. Classification of Metamorphic Rocks

35. Gneiss Typically Displays a Banded Appearance

36. Marble—A Nonfoliated Metamorphic Rock