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Title: Rocks

Chapter 3
  • Rocks

Section 3.1
  • Rock A rock is any solid mass of mineral or
    mineral-like matter that occurs naturally as part
    of our planet.
  • Most rocks contain multiple types of minerals.
    Each mineral retains its properties within the
  • There are 3 major types of rocks Igneous,
    Sedimentary, and Metamorphic.

The Rock Cycle
Interactions among Earths water, air, and land
can cause rocks to change from one type to
another. This continuous process that causes
rocks to change is the Rock Cycle.
The Rock Cycle-Sedimentary Rocks
Sedimentary Rock A rock formed by the compaction
and cementation of sediments. Weathering
Process where rocks are physically and/or
chemically broken down by water, air, and living
things. The weathered pieces are called
sediments. Weathering and Erosion can change any
rock into a sedimentary rock.
The Rock Cycle-Metamorphic Rocks
Metamorphic Rock A rock altered by heat and
pressure. Heat and Pressure and can change any
rock into a metamorphic rock. .
The Rock Cycle-Igneous Rocks
Igneous Rock A rock formed by the solidification
of magma. Magma-molten material that forms deep
beneath the Earths surface. Lava-Magma that
reaches the surface In order to become an
igneous rock, magma must cool beneath the surface
or as a result of a volcanic eruption becomes an
igneous rock.
The Earth as a System
  • Processes driven by heat from the Earths
    interior are responsible for forming both igneous
    and metamorphic rocks.
  • Weathering and the movement of weathered
    materials by water, gravity, glaciers, and wind
    are external processes powered by the energy from
    the sun. External processes produce sedimentary

  • 1. What is a rock?
  • 2. What are the three major types of rocks?
  • 3. What is the rock cycle?
  • 4. What powers the Earths rock cycle?
  • 5. How might a sedimentary rock become an igneous

Igneous Rocks
  • Igneous Rocks forms from the solidification and
    crystallization of magma or lava.
  • There are two types of igneous rocks.
  • Intrusive
  • Extrusive

Intrusive Igneous Rocks
  • Intrusive Igneous Rocks form when magma
    solidifies under the Earths surface.
  • Magma is less dense than the surrounding rocks,
    so it slowly works its way toward the surface.
  • As it rises, it cools it allows elements to
    combine and form minerals. Since the magma cools
    slowly, the minerals are able to grow in size.

Intrusive Igneous Rocks
Diorite (Left) and Granite (Right) are both
examples of intrusive igneous rocks. The slow
cooling of magma beneath the Earths surface
allows the growth of large mineral crystals.
Extrusive Igneous Rocks
  • Extrusive Igneous Rocks form when lava solidifies
    above the Earths surface.
  • Since the lava cools much quicker above the
    Earths surface, the minerals in extrusive
    igneous rocks are not able to grow as large.

Extrusive Igneous Rocks
Rhyolite (Left) and Basalt (Right) are both
examples of extrusive igneous rocks. The rapid
cooling of lava resulted in a rock with small,
interconnected mineral grains.
Classification of Igneous Rocks
  • Texture and composition are two characteristics
    used to classify igneous rocks.
  • The rate of cooling strongly affects the type
  • Texture Classifications Coarse-Grain,
    Fine-Grain, Glassy, and Porphritic
  • Composition Classifications Granitic, Basaltic,
    Other Compositions

Texture Classifications
  • Coarse-Grain Texture The slow cooling of magma
    allows the formation of large crystals.
  • Fine-Grain Texture The rapid cooling of magma or
    lava results in small, interconnected mineral

Texture Classifications
  • Porphyritic TExture Minerals do not form at the
    same rate so it is possible for some minerals to
    become quite large before others begin to form.
    These large crystals that are surrounded by fine
    grained minerals are called phenocyrsts.
  • Glassy Texture When lava is spewed onto the
    surface, ions dont have time to arrange
    themselves into crystals and the result is a
    glassy texture.

Composition Classifications
  • Granitic Composition Igneous rocks that are made
    almost entirely of the light-colored silicate
    minerals quartz and feldspar.
  • Granitic rocks are the major rocks of the
    continental crust.

Rhyolite is an extrusive granitic rock. Notice
that is light in color
Composition Classification
  • Basaltic Composition Rocks that contain many
    dark silicate minerals and plagioclase feldspar.
  • They are rich in iron which makes them darker and
    denser than granitic rocks.

Gabbro is an intrusive igneous rock with basaltic
Composition Classification
  • Other compositional groups Rocks with a
    composition between granitic and basaltic have an
    andesitic composition. They contain at least 25
    dark silicate minerals.
  • Ultramafic Peridotite is an important igneous
    rock that is composed mostly of olivine and some
    pyroxene. It is composed almost entirely of dark
    silicate minerals so its composition is referred
    to as ultramafic.

Classification of Igneous Rocks
Sedimentary Rocks
  • All sedimentary rocks form when existing rocks
    are broken down into sediments.
  • These sediments are compacted and cemented

Weathering, Erosion, Deoposition
  • Weathering Chemical or physical breakdown of
    rock into smaller pieces called sediments.
  • Erosion The carrying away of the sediments by
    agents such as water, wind, ice, or gravity.
  • Deposition When the agent loses energy and drops
    the sediments. Sediments are deposited according
    to size.
  • Large sediments are deposited first.

Compaction and Cementation
  • Compaction and cementation turns sediments into
    sedimentary rock.
  • Compaction is a process that squeezes sediments.
    It is caused by the weight of the sediments.
  • Cementation takes place when dissolved minerals
    are deposited in the tiny spaces among the

Classification of Sedimentary Rocks
  • Sedimentary rocks can be classified into two main
    groups according to the way they form.
  • Clastic Sedimentary Rocks Made of weathered bits
    of rocks and minerals.
  • Chemical/Biochemical Sedimentary Rocks Forms
    when dissolved minerals precipitate from water

Clastic Sedimentary Rocks
  • Grouped according to the size of the sediments in
    the rocks.

Clastic Sedimentary Rocks
Conglomerate is a clastic sedimentary rock that
contains large (greater then two millimeters in
diameter) rounded particles.
Sandstone is a clastic sedimentary rock made up
mainly of sand-size (1/16 to 2 millimeter
diameter) weathering debris
Siltstone is a clastic sedimentary rock that
forms from silt-size (between 1/256 and 1/16
millimeter diameter) weathering debris.
Shale is a clastic sedimentary rock that is made
up of clay-size (less then 1/256 millimeter in
diameter) weathering debris
Chemical and Biochemical Sedimentary Rocks
  • The precipitation that forms chemical sedimentary
    rocks occurs when the water evaporates or boils
    off leaving a solid product.

Rock Salt is a chemical sedimentary rock that
forms from the evaporation of ocean or saline
lake waters
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Features of Sedimentary Rocks
  • The many unique features of sedimentary rocks are
    clues to how, when, and where the rocks formed.
  • In undisturbed sedimentary rocks, the oldest
    layer of deposition is at the bottom and the
    youngest is at the top.
  • Ripple marks and mud cracks can give clues as to
    the environment that the rock formed in

Features of Sedimentary Rocks
  • Fossils traces or remains of ancient life are
    unique to some sedimentary rocks such as
  • Fossils play a key role in matching up rocks from
    different places that are the same age.
  • Fossils can be used to help answer questions
    about the rocks that contain them such as did the
    rock form in land or water? Was the climate hot
    or cold? When did the rock form?

Metamorphic Rocks
  • Form when existing rocks are changed by heat and
    pressure, usually a few kilometers below the
    Earths surface and extend to the upper mantle.
  • Often the changed rock looks different and has a
    different chemical composition than the parent
    rock (parent rockoriginal rock).
  • There are two types of metamorphism Contact and

Contact Metamorphism
  • Contact Metamorphism Hot magma moves into rock
    causing contact metamorphism to take place.
  • Produces low-grade metamorphism which are minor
    changes in the rock. Example Marble

Regional Metamorphism
  • Regional Metamorphism During mountain building,
    large areas of rocks are subjected to extreme
    pressure and temperatures.
  • Produces high-grade metamorphism and large-scale

Which Metamorphism is it?
Agents of Metamorphism
  • The agents of metamorphism are heat, pressure,
    and hydrothermal solutions.
  • Heat The most important agent because it
    provides energy to drive chemical reactions.
  • Two sources of heat Magma and depth
  • Pressure Just like temperature, pressure
    increases with depth. Pressure causes the spaces
    between mineral grains to close.
  • Hydrothermal Solutions Hot, water based
    solutions that escape from magma. Promote
    recrystallization by dissolving minerals and
    depositing new ones.

Classifications of Metamorphic Rocks
  • Like igneous rocks, metamorphic rocks are
    classified based on texture and composition.
  • There are two groups foliated and nonfoliated

Foliated Metamorphic Rocks
  • When rocks undergo contact metamorphism, they
    become more compact and dense. The pressure
    causes minerals to align in a similar direction.
    This gives the rock a layered or banded
  • Under extreme conditions, minerals recrystallize
    with a preferred orientation-at a right angle to
    the direction of force.

Foliated Metamorphic Rocks
Gneiss is foliated metamorphic rock that has a
banded appearance and is made up of granular
mineral grains. It typically contains abundant
quartz or feldspar minerals
Nonfoliated Metamorphic Rocks
  • A metamorphic rock that does not have a banded
  • Most nonfoliated rocks contain only one mineral.

Nonfoliated Metamorphic Rocks
Marble is a non-foliated metamorphic rock that is
produced from the metamorphism of limestone. It
is composed primarily of calcium carbonate
Quartzite is a non-foliated metamorphic rock that
is produced by the metamorphism of sandstone. It
is composed primarily of quartz
Classification of Major Metamorphic Rocks