Prentice Hall EARTH SCIENCE

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Prentice Hall EARTH SCIENCE

• Tarbuck Lutgens

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Chapter 3
Rocks
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3.1 The Rock Cycle
? Rocks are any solid mass of mineral or
mineral-like matter occurring naturally as part
of our planet.
? Types of Rocks
1. Igneous rock is formed by the crystallization
of molten magma.
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3.1 The Rock Cycle
? 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
of pre-existing rock deep within Earth (but still
in the solid state) by heat, pressure, and/or
chemically active fluids.
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3.1 The Rock Cycle
? Shows the interrelationships among the three
rock types (igneous, sedimentary, and metamorphic)
? Magma is molten material that forms deep
beneath the Earths 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.
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The Rock Cycle
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3.1 The Rock Cycle
? Processes driven by heat from the Earths
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.
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3.2 Igneous Rocks
1. Intrusive igneous rocks are formed when magma
hardens beneath Earths surface.
2. Extrusive igneous rocks are formed when lava
hardens.
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3.2 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, interconnected
mineral grains.
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Course-Grained Igneous Texture
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Fine-Grained Igneous Texture
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3.2 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.
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Obsidian Exhibits a Glassy Texture.
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Porphyritic Igneous Texture
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3.2 Igneous Rocks
2. Composition (continued)
Basaltic composition rocks are made mostly of
dark-colored silicate minerals and plagioclase
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.
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Basalt
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Classification of Igneous Rocks
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3.3 Sedimentary Rocks
? Weathering, Erosion, and Deposition
Erosion involves the weathering and the
removal of rock.
Deposition occurs when an agent of
erosionwater, wind, ice, or gravityloses energy
and drops sediments.
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3.3 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.
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3.3 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
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Shale with Plant Fossils
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Conglomerate
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3.3 Sedimentary Rocks
? Two Main Groups
2. Chemical sedimentary rocks form when dissolved
substances precipitate, or separate, from water.

• Common rocks include

- limestonemost abundant chemical rock
- microcrystalline quartz known as chert, flint,
jasper, or agate
- evaporites such as rock salt or gypsum
- coal
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Fossiliferous Limestone
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Classification of Sedimentary Rocks
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3.3 Sedimentary Rocks
? Features of sedimentary rocks are clues to how
and where the rocks are formed
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3.4 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 Earths surface and extend
into the upper mantle.
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3.4 Metamorphic Rocks
? Contact metamorphism occurs when magma moves
into rock.

• Occurs near a body of magma

• Changes are driven by a rise in temperature.

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3.4 Metamorphic Rocks
? Dynamic metamorphism often results in a change
in texture of the rock with little or no change
in mineral content.  The resulting texture is
that of finely pulverized rock powder called
MYLONITE

• Occurs where major faults slip past each other
• Allows for a type of high-pressure/low-temperature
  metamorphism

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3.4 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

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3.4 Metamorphic Rocks

• Progressive metamorphism The recrystallization of
  a rock in response to an increase in the
  intensity of metamorphism, i.e. pressure and
  temperature.
• Rocks closer to the stress will demonstrate more
  crystallization than a rock farther away.

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3.4 Metamorphic Rocks
? Heat

• Provides the energy needed to drive chemical
  reactions

? Pressure

• Causes a more compact rock with greater density

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Origin of Pressure in Metamorphism
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3.4 Metamorphic Rocks
? Hydrothermal Solutions

• Hot water-based solutions escaping from the mass
  of magma

• Promote recrystallization by dissolving original
  minerals and then depositing new ones

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3.4 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

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Classification of Metamorphic Rocks
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Gneiss Typically Displays a Banded Appearance
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MarbleA Nonfoliated Metamorphic Rock