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.
• What makes up the solid parts of Earth

? 3 Types of Rocks
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3.1 The Rock Cycle
? Types of Rocks

• Igneous rock is formed by the crystallization of
  molten magma.
• The word is Latin for from Fire
• It FORMS when Magma or molten rock cools and
  hardens
• Magma is called lava when its exposed at Earths
  surface

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Sedimentary rock

• 2. Sedimentary rock is formed from the weathered
  products of preexisting rocks that have been
  transported, deposited, compacted, and cemented.
• Erosion (wind, waves etc) break down ALL types of
  rock into pieces/fragments which is known as
  sediment.

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Metamorphic rock

• 3. Metamorphic rock is formed by the alteration
  of pre-existing rock deep within Earth (but still
  in the solid state)
• Forces and process (tremendous pressure, extreme
  heat, and chemical processes) Change the FORM of
  existing rock.
• The word metamorphic means changes form
• Any of the 3 major types can be changed into
  another of the 3

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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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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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Bowens Reaction Series

• Early 1900s Canadian geologist N. L. Bowen began
  studying how minerals crystallize from magma.
• HE LEARNED that as magma cools, certain minerals
  tend to crystalize first.
• Minerals crystallize in a predictable order, over
  a large temperature range

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These sequences could be assembled into a
composite sequence.
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Bowens hypothesis

• Minerals form in 2 ways
• 1) gradual, continous formation of minerals that
  have similar chemical compositions
• 2) sudden changes in mineral types
• The pattern of mineral formation depends on the
  chemical composition of the magma

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Chemical Stability/Physical Stability of Minerals
and Rocks

• Chemical Stability is a measure of the tendency
  of a chemical compound that maintains the
  original mineral composition.
• Minerals that are most resistant to weathering
  have the highest number of bonds.
• Pg. 128
• Write in Cornell Notes why is Devils Postpile
  broken down into columns?

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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
? Three 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
? Three 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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3rd class

• Organic Sedimentary Rocks
• Forms from the remains of living things.
• Exa. Coal, some limestones
• Form when marine organisms such as coral, clams,
  oysters and plankton remove chemical components
  of the minerals calcite and aragonite from the
  seawater.
• Organisms make shells from aragonite when they
  die the shell becomes limestone.
• Chalk is an example

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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
? 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
? 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