What is a rock?

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What is a rock?

• A rock is a combination of minerals. For example
  Granite is composed of biotite, quartz, and
  feldspar.

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The Rock Cycle
Metamorphic Rocks

• Any rock can be changed into any other type of
  rock.
• The rock cycle is the continuous changing and
  remaking of rocks.

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The Rock Cycle

• Igneous and sedimentary rocks may be transformed
  by heat, pressure and chemical reactions into
  metamorphic rocks.
• Metamorphic rocks may be changed or metamorphosed
  into other metamorphic rocks. They may also be
  remelted into and igneous rock. Or a metamorphic
  rock can be weathered to form a sedimentary rock.
• Any rock can be changed into any other type of
  rock.

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Other Possible Paths
Metamorphic Rocks

• There is more than one path in the rock cycle.

• The rocks of Earths crust are constantly being
  recycled from one type to another.
• The processes that help shape Earths
  landscapes are also part of the rock cycle.

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What are igneous rocks?
What are igneous rocks?

• About 95 of rocks on the earth are igneous or
  metamorphic although mostly sedimentary cover the
  surface due to weathering and erosion.
• Igneous rocks are rocks are formed from volcanoes
• Igneous rocks are formed from the crystallization
  of magma

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Types of Igneous Rocks
What are igneous rocks?

• Intrusive igneous rocks are coarse-grained
  igneous rocks that cool slowly beneath Earths
  surface. (INside the earth)

• Granite is the most common intrusive igneous
  rock.

• Extrusive igneous rocks are fine-grained igneous
  rocks that cool quickly on Earths surface.
  (ExOut of)
• An example is basalt or obsidian.

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Types of Igneous Rocks
What are igneous rocks?

• Careful study of granite rock formations revealed
  that they cut across other rock formations.

• These cross-cutting relationships are evidence
  that the granite was intruded, or forced into,
  existing rocks.

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Composition of Magma
What are igneous rocks?

• Magma is often a slushy mix of molten rock,
  gases, and mineral crystals.

• The elements found in magma are the same major
  elements found in Earths crust oxygen (O),
  silicon (Si), aluminum (Al), iron (Fe), magnesium
  (Mg), calcium (Ca), potassium (K), and sodium
  (Na).

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Classifying Igneous Rocks
Classifying Igneous Rocks

• Igneous rocks are broadly classified as intrusive
  or extrusive.

• Igneous rocks are further classified by their
  mineral compositions and texture.
• Composition refers to the minerals that make up a
  rock.

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Mineral Composition
Classifying Igneous Rocks

• The two main groups of igneous rocks are felsic
  and mafic are classified according to their
  mineral compositions.

• Felsic rocks, such as granite, are light-colored
  and have high silica contents. (LLight!)

• Mafic rocks, such as gabbro, are dark-colored,
  have lower silica contents, and are rich in iron
  and magnesium.

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Grain Size
Classifying Igneous Rocks

• In addition to differences in their mineral
  compositions, igneous rocks differ in the sizes
  of their grains.

Cooling Rates

• When lava flows on Earths surface, it cools
  quickly and there is not enough time for large
  crystals to form.
• Extrusive igneous rocks have no visible mineral
  grains.
• When magma cools slowly beneath Earths surface,
  there is sufficient time for large crystals to
  form.
• Intrusive igneous rocks may have crystals larger
  than 1 cm.

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Texture
Classifying Igneous Rocks

• Often, its easier to observe the sizes of
  mineral grains than it is to observe their
  shapes.

• Many mineral grains have interlocking edges.
• As the grains crystallize from magma, they grow
  together and form irregular edges.
• Texture gives clues for the identification of
  various igneous rocks.
• Texture is the size, shape, arrangement and
  distribution of minerals in the rock.

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Glassy Texture

• An example of glassy texture is obsidian.

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Fine grained texture

• An example of fine grained is basalt or gabbro.

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Coarse grained texture

• An example is granite.

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Texture
Classifying Igneous Rocks

• Porphyritic Texture

• A rock that has a porphyritic texture is
  characterized by large crystals surrounded by
  finer-grained crystals.

• Porphyritic textures indicate a complex cooling
  history wherein a slowly cooling magma suddenly
  began cooling rapidly.

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Pumice

• Pumice can float!
• Pumice is used as an abrasive cleaner.

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More Uses of Igneous Rocks
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Uses of Igneous rocks- granite countertops
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Scoria is a landscaping material
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Igneous Rocks

• Igneous rock - Wikipedia, the free encyclopedia

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Metamorphic Rocks

• Metamorphic rock - Wikipedia, the free
  encyclopedia

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Uses of Metamorphic Rocks

• Marble chips for landscaping

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Igneous Rocks as Resources
Classifying Igneous Rocks

• Igneous rocks have several characteristics that
  make them especially useful as building materials.

• The interlocking grain textures of igneous rocks
  help to give them strength.
• Many of the minerals found in igneous rocks are
  resistant to weathering.

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Ore Deposits
Classifying Igneous Rocks

• Ores are minerals that contain a useful substance
  that can be mined at a profit.

• Valuable ore deposits are often associated with
  igneous intrusions.
• These deposits sometimes occur as veins.

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Section Assessment
Classifying Igneous Rocks

• 1. Match the following terms with their
  definitions.
• ___ felsic
• ___ mafic
• ___ ultramafic
• ___ porphyritic

A. igneous rocks that have low silica content and
very high levels of iron and magnesium B. igneous
rocks that are light-colored, have high silica
contents, and contain quartz and
feldspars C. texture characterized by well-formed
crystals surrounded by finer-grained
crystals D. igneous rocks that are dark-colored,
have lower silica contents, and are rich in iron
and magnesium
B D A C
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End of Section 2
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Chapter Resources Menu
Chapter Resources Menu

• Study Guide
• Section 5.1
• Section 5.2
• Chapter Assessment
• Image Bank

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Section 5.1 Main Ideas
Section 5.1 Study Guide

• Igneous rocks are formed by the cooling and
  crystallization of magma. Intrusive rocks form
  inside Earths crust, and extrusive rocks form on
  Earths surface. Extrusive rocks, which cool more
  rapidly than intrusive rocks, are generally more
  fine grained.

• Magma is a slushy mix of molten rock, gases, and
  mineral crystals. The elements found in magma are
  the same major elements found in Earths crust
  oxygen (O), silicon (Si), aluminum (Al), iron
  (Fe), magnesium (Mg), calcium (Ca), potassium
  (K), and sodium (Na).

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Section 5.1 Main Ideas
Section 5.1 Study Guide

• Silica (SiO2) is the most abundant compound in
  magma. Magmas are classified as basaltic,
  andesitic, and rhyolitic, based on the amount of
  SiO2 they contain.

• Different minerals melt and crystallize at
  different temperatures in the processes of
  partial melting and fractional crystallization.
  Minerals crystallize from magma in a sequential
  pattern known as Bowens reaction series.

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Section 5.2 Main Ideas
Section 5.2 Study Guide

• Igneous rocks are classified as felsic, mafic,
  intermediate, and ultramafic, depending upon
  their mineral compositions. Felsic rocks such as
  granite are light-colored, have high silica
  contents, and contain quartz and feldspars. Mafic
  rocks such as gabbro are dark-colored, have lower
  silica contents, and are rich in iron and
  magnesium. Intermediate rocks have moderate
  silica levels. Ultramafic rocks have low silica
  contents and very high levels of iron and
  magnesium. Igneous groups can be further
  identified by crystal size and texture.

• Early forming minerals may have well-shaped
  crystals, while later-forming minerals have
  irregular shapes. Porphyritic textures contain
  both large and small crystals.

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Section 5.2 Main Ideas
Section 5.2 Study Guide

• Igneous rocks such as granite are often used as
  building materials because of their strength,
  durability, and beauty.

• Valuable ore deposits and gems are often
  associated with igneous intrusions. Ores of rare
  elements such as lithium and beryllium are found
  in veins of extremely large-grained minerals
  called pegmatites. Diamonds are found in rare
  types of igneous intrusions known as kimberlites.

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Multiple Choice
Chapter Assessment

• 1. The process wherein different minerals form at
  different temperatures is called ____.
• a. partial melting
• b. Bowens reaction series
• c. fractional crystallization
• d. crystal separation

Partial melting is when some minerals melt at low
temperatures while others remain solid. Bowens
reaction series describes in what order minerals
form. Crystal separation is a hypothesis that
answers questions about Bowens reaction series.
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Multiple Choice
Chapter Assessment

• 5. Extrusive igneous rocks generally have small
  mineral grains because ____.
• a. they cool slowly.
• b. the minerals in extrusive rocks do not form
  crystals under any condition.
• c. they cool quickly.
• d. there is too much water in the magma.

By quickly cooling, the minerals in extrusive
igneous rocks do not have enough time to form
large crystals.
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Short Answer
Chapter Assessment

• 6. What characteristics make igneous rocks useful
  as building materials?

Igneous rocks are useful as building materials
because the interlocking grain textures of
igneous rocks help to give them strength and many
of the minerals found in igneous rocks are
resistant to weathering.
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Short Answer
Chapter Assessment

• 7. What causes a porphyritic texture to form in
  certain rocks?

A porphyritic texture indicates a complex cooling
history wherein a slowly cooling magma suddenly
began cooling rapidly.
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Chapter 5 Images
Image Bank
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Chapter 5 Images
Image Bank
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Chapter 5 Images
Image Bank