1. 3.2 Rocks

2. What is a rock?
Rocks are any solid mass of mineral or mineral-like matter occurring naturally as part of our planet.
The three major types of rocks are igneous, sedimentary and metamorphic rocks
Interactions among Earth’s water, air, and land can cause rocks to change from one type to another
The continuous processes that cause rocks to change make up The Rock Cycle

3. The Rock Cycle
Most changes in the rock cycle take place over long periods of time
Types of Rocks
Igneous rock is formed when magma cools and crystallizes beneath the surface or as a result of a volcanic eruption

4. The Rock Cycle
2. Sedimentary rock is formed from the weathered products of preexisting rocks that have been transported, deposited, compacted, and cemented

5. The Rock Cycle
3. Metamorphic rock is formed by the alteration of pre-existing rock deep within Earth by HEAT, PRESURE, and/or CHEMICALLY ACTIVE FLUIDS

6. The Rock Cycle
The Rock Cycle shows how the three rock types are related to each other
Terms to know:
Magma is molten material that forms deep beneath 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 weather pieces of Earth materials

8. The Rock Cycle Energy that drives the Rock Cycle
Processes driven by heat from the Earth’s interior are responsible for forming both igneous and metamorphic rock
Weathering and movement of weathered material are EXTERNAL processes powered by energy from the Sun
External processes produce sedimentary rock

9. Bowen’s Reaction Series
As magma cools, elements in it bond together to form crystals of minerals
Not all minerals form at same temperature during cooling
Some grow when it is hot
Others grow when magma is cooler
Bowen’s Reaction series shows when different minerals form as magma cools

10. If olivine allowed to cool further, olivine would react with the residual magma and change to pyroxene.
With dropping temp. we have decreasing thermal vibration of molecules, allows silica to form more complex structures

11. Igneous Rocks
Recall that igneous rocks form when magma or lava cools or hardens
In the picture to the right, a dark-colored igneous rock called Basalt will form
Different rock would have been made if it would have stayed inside Earth

12. Formation of Igneous Rocks
Rock formed when magma hardens beneath Earth’s surface are known as Intrusive igneous rocks
Cooling below the surface is very SLOW, forming large crystals in the rock

13. Formation of Igneous Rocks
When lava hardens, the rocks that form are called Extrusive Igneous Rocks
Cooling at the surface is much FASTER, thus making SMALLER crystals in the rock

14. Classification of Igneous Rocks
Igneous rocks can be classified based on their composition and texture
Composition is what they’re made of or the amounts of light and dark minerals in the rock
Texture describes the appearance based on its size, shape and arrangement of crystals

15. Classification of Igneous Rocks
Texture
Coarse-grained is caused by SLOW cooling resulting in LARGER crystals (known as Phaneritic texture)
Fine-grained texture is caused by RAPID cooling in SMALLER, interconnected mineral grains (known as Aphanitic texture)

16. Phaneritic Igneous Texture
Example: Granite

17. Aphanitic Igneous Texture
Example: Rhyolite

18. Classification of Igneous Rocks
Texture (continued)
Glassy texture is caused by VERY RAPID cooling (ex. Obsidian)
Porphyritic texture is a mixture of both large and small crystals (ex. Andesite)
Phenocrysts – larger crystals surrounded by a background of smaller crystals

19. Classification of Igneous Rocks
Composition
Felsic composition rocks are made mostly of light- colored quartz and feldspar silicate minerals
Felsic rocks are the MAJOR ROCKS of the continental crust
Examples are Granite (intrusive) and Rhyolite (extrusive)

20. Classification of Igneous Rocks
Composition (continued)
Intermediate composition rocks are between granitic light-color minerals and mafic composition
Examples are Andesite (extrusive) and Diorite (intrusive)

21. Classification of Igneous Rocks
Composition
Mafic composition rocks are made MOSTLY of dark- colored silicate minerals and plagioclase feldspar
Typically DARKER and DENSER than Felsic rocks
Examples are Basalt (extrusive) and Gabbro (intrusive)

22. Classification of Igneous Rocks
Composition
Ultramafic composition rocks are made mostly of iron and magnesium- rich minerals
Rare at Earth’s surface
Examples are Komatiite (extrusive) and Peridotite (Intrusive)

23. ONE LAST IMPORTANT POINT
For Igneous rocks
The amount of silica content changes (SiO2)
Mafic/Ultramafic rocks have the least amount of silica content
Felsic rocks have the most amount of silica content
This is all due to the minerals that they are made of

25. Sedimentary Rocks
All sedimentary rock begin to form when existing rocks break down into sediments
Sediments, which is weathered rock debris, are often transported around

26. Formation of Sedimentary Rocks
1st Step - Weathering
Any process hat breaks up rocks into sediments
Physical weathering is when physical forces break up rocks
Chemical weathering is when minerals in the rocks change into new substances

27. Formation of Sedimentary Rocks
2nd Step – Erosion Involves the WEATHERING and the REMOVAL of rock
Agents of erosion:
Air
Water
Wind
Gravity
3rd Step - Deposition occurs when an agent of erosion loses energy and drops sediments
Deposited according to size (large to small)

28. Formation of Sedimentary Rocks
4th Step – 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
HINT: Glue together

29. Classification of Sedimentary Rocks
Classified into groups according to the WAY THEY FORM
Three main groups
Clastic
Chemical
Organic

30. Classification of Sedimentary Rocks
Three Main Groups
Clastic sedimentary rocks are composed of weathered bits of rocks and minerals
Classified by particle size
Common rocks include:
Shale (most abundant)
Sandstone
Conglomerate

31. Classification of Sedimentary Rocks
Three main groups
2. Chemical Sedimentary rocks form when dissolved precipitate (separate from water)
Common rocks include:
Limestone – most abundant chemical rock
Evaporites such as rock salt or gypsum
Coal

32. Classification of Sedimentary Rocks
Three main groups
3. Organic Sedimentary Rocks
Some are the shells and skeletal remains of organisms that settle to the ocean floor
Examples include coquina, limestone, and chalk

33. Features of Some Sedimentary Rocks
The many unique features of sedimentary rocks are clues to how, when, and where they formed
Some features include layering, and fossils

34. Features of Some Sedimentary Rocks
Sedimentary rock layering
Graded bedding – when different sizes and shapes of sediment settle to different levels in the rock
Cross bedding – the slanting of layers in sedimentary rocks

35. Sedimentary Rock Chart

36. 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

37. Formation of Metamorphic Rocks
Most metamorphism occurs in one of two settings:
Contact metamorphism
Regional metamorphism

38. Formation of Metamorphic Rocks
Contact metamorphism occurs when magma move into rock
Happens near a body of magma
Changes are driven by a rise in temperature
Example: Marble forms when magma intrudes a limestone body

39. Formation of Metamorphic Rocks
Regional metamorphism is metamorphism of rocks over a large area
During mountain building, large areas of rocks are subjected to extreme pressures and temperatures
Produces a large amount of metamorphic rock

40. Agents of Metamorphism
The agents of metamorphism are:
Heat
Pressure
Hydrothermal solutions

41. Agents of Metamorphism
Heat (most important)
Provides the energy needed to drive chemical reactions
Heat comes from magma and the change in temperature with depth
Pressure
Causes a more compact rock with greater density
Pressure also increases with depth

42. Origin of Pressure in Metamorphism

43. Agents of Metamorphism
Hydrothermal solutions
Hot water-based solutions escaping from the mass of magma
Promote recrystallization by dissolving original minerals then depositing new ones

44. Classification of Metamorphic Rocks
Two main categories
Foliated Metamorphic Rock
Has a banded or layered appearance
Ex. Gneiss
Nonfoliated Metamorphic Rock
Does not have a banded texture
Ex. Marble

45. Metamorphic Rock Chart