Rocks

1
Chapter 3

• Rocks

2
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
  rock.
• There are 3 major types of rocks Igneous,
  Sedimentary, and Metamorphic.

3
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.
4
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.
5
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. .
6
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.
7
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
  rocks.

8
Questions

• 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
  rock?

9
Igneous Rocks

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

10
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.

11
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.
12
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.

13
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.
14
Classification of Igneous Rocks

• Texture and composition are two characteristics
  used to classify igneous rocks.
• The rate of cooling strongly affects the type
  texture.
• Texture Classifications Coarse-Grain,
  Fine-Grain, Glassy, and Porphritic
• Composition Classifications Granitic, Basaltic,
  Other Compositions

15
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
  grains.

16
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.

17
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
18
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.
19
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.

20
Classification of Igneous Rocks
21
Sedimentary Rocks

• All sedimentary rocks form when existing rocks
  are broken down into sediments.
• These sediments are compacted and cemented
  together.

22
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.

23
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
  sediments.

24
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
  solutions.

25
Clastic Sedimentary Rocks

• Grouped according to the size of the sediments in
  the rocks.

26
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
27
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
28
(No Transcript)
29
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

30
Features of Sedimentary Rocks

• Fossils traces or remains of ancient life are
  unique to some sedimentary rocks such as
  limestone.
• 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?

31
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
  Regional

32
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

33
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
  deformation.

34
Which Metamorphism is it?
35
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.

36
Classifications of Metamorphic Rocks

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

37
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
  appearance.
• Under extreme conditions, minerals recrystallize
  with a preferred orientation-at a right angle to
  the direction of force.

38
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
39
Nonfoliated Metamorphic Rocks

• A metamorphic rock that does not have a banded
  texture.
• Most nonfoliated rocks contain only one mineral.

40
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
41
Classification of Major Metamorphic Rocks