chapter: earth materials table of contents section 2: igneous rocksigneous rocks section 1: minerals...

Chapter: Earth Materials

Table of ContentsTable of Contents

Section 2: Igneous Rocks

Section 1: Minerals

Section 3: Sedimentary Rocks

Section 4: Metamorphic Rocks and the Rock Cycle

• The crust is the outermost layer of Earth.

Common Elements

MineralsMinerals

11

Composition of Earth’s Crust

• A mineral is a naturally occurring element or compound that is inorganic, solid, and has a crystalline structure.

MineralsMinerals

11 What’s a Mineral?

• A mineral has a characteristics set of physical properties, but some of these properties can differ from sample to sample.

MineralsMinerals

11 Physical Properties

• Some physical properties are controlled by the orderly arrangement of atoms in a mineral’s structure.

MineralsMinerals

11 Atom Arrangement

• The arrangement of atoms and the bonds between them can reflect the way a mineral breaks, how hard it is, and what types of crystal shape it has.

• Minerals break along planes that cut across relatively weak chemical bonds, a smooth, flat surface is created. This is called cleavage.

MineralsMinerals

11 Atom Arrangement

• Some minerals do not split along well-defined flat surfaces. In such cases, a mineral will break unevenly. This type of irregular break is called fracture.

• The physical property that measures resistance to scratching is called hardness.

MineralsMinerals

11 Hardness

Luster and Streak

MineralsMinerals

11

• The way a mineral reflects light is the physical property known as luster.

• Metallic and nonmetallic.

• Metallic luster minerals reflect light in a way that a metal surface might.

MineralsMinerals

11 Luster and Streak

• Nonmetallic luster, includes minerals that shine like glass or appear earthy or waxy.

• The color of mineral in powdered form is called streak.

MineralsMinerals

11 Crystal Shape• The orderly internal arrangement of

atoms in a mineral often is indicated by its external crystal shape.

• The types of symmetry shown by the crystal are key elements in determining the crystal system to which a mineral belongs.

MineralsMinerals

11 Mineral Formation

• Growth also is controlled by how fast atoms can migrate to the crystal and by the temperature and pressure conditions of the surroundings.

MineralsMinerals

11 Minerals From Hot Water

• Some minerals are produced from hot water solutions rich in dissolved mineral matter.

• When hot water passes through cracks in cooler rock, minerals may form within the cracks.

MineralsMinerals

11 Minerals from Magma

• Molten rock material found inside Earth is called magma.

• As magma cools, atoms slow down and begin to arrange into an orderly structure.

• Below the solidification temperature of a mineral, crystals of that particular mineral may form and grow.

MineralsMinerals

11 Minerals From Evaporation

• When water slowly evaporates, concentrated dissolved mineral may be left behind to form crystal.

MineralsMinerals

11 Mineral GroupsSilicates

• Silica is a common term for a compound that contains silicon plus oxygen or silicon dioxide (SiO2).

MineralsMinerals

11 Silicate Structures

• The simplest silicate structures have silicon-oxygen tetra-hedrons that are not linked together.

• By joining silicon-oxygen tetrahedrons together, chains, sheet, and three-dimensional framework structures can form.

MineralsMinerals

11 Silicate Structures

• Quartz and feldspar group silicates make up most of Earth’s continental crust.

• Earth’s oceanic crust is denser and contains a larger percentage of silicates whose tetrahedrons are not linked together as much.

MineralsMinerals

11 Important Non-silicates • Many important mineral groups are

not silicates.

• These include the carbonates, oxides, halides, sulfides, sulfates, and native metals.

• The non-silicate groups are a source of many valuable ore minerals and building materials.

MineralsMinerals

11 Important Non-silicates

• To be an ore, a mineral must occur in large enough quantities to be economically recoverable.

Section CheckSection Check

11Question 1

Which is NOT a mineral?

A. apatieB. flouriteC. goldD. oxygen


11Answer

The answer is D. A mineral must be a solid.


11Question 2

Which is NOT a physical property of minerals?

A. cleavageB. fractureC. hardnessD. Mohs

11Section CheckSection Check

AnswerThe answer is D. Mohs is a scale used to determine the hardness of a mineral.


11Question 3

How many crystal shapes have been identified?

A. fiveB. sixC. sevenD. eight

11Section CheckSection Check

Answer

The answer is B. Minerals can be classified by these six shapes.

Igneous RocksIgneous Rocks

22

• A rock is a naturally formed consolidated mixture containing minerals, rock fragments, or volcanic glass.

What’s a rock?

• Rocks are identified by their composition and texture.

• Texture is a description that includes the size and arrangement of the rock’s components.


22

• Igneous rocks are those that form from molten rock material called magma.

Intrusive Igneous Rocks

• Such rocks also are called intrusive igneous rocks because they form within, or push into, regions of Earth’s crust.


22

• As it passes through rock, magma might cause partial melting of the rock it intrudes.

Nature of Magma

• Geologists have learned that minerals melt at different temperatures, so some will melt when exposed to the thermal energy of the magma.


22

• As crystals solidify in cooling magma, they use up certain atoms.

Nature of Magma

• High-temperature magmas tend to crystallize first.


22 Nature of Magma

to solidify at lower temperatures and float to the top of the magma chamber.

• Late-forming, less dense minerals tend


22

• The composition of intrusive igneous rocks gives you clues as to where in Earth they formed.

Nature of Magma

• Igneous rocks with abundant quartz generally are associated with continental crust.

• Those with little or no quartz generally are associated with deep locations in continental crust or with oceanic crust.


22

• In intrusive igneous rocks, grain size, which means the size of individual mineral crystals, gives you clues as to how fast magma cooled.

Intrusive Igneous Rock Texture

• Magma that cools slowly, allows atoms time to migrate about and form large crystals.


22

• Rocks that are quartz-rich and contain potassium feldspar and plagioclase feldspar are called granite.

Classification of Intrusive Igneous Rocks

• Rocks with no quartz and abundant plagioclase feldspar and pyroxene are called gabbro.

• Peridotite is denser than gabbro, is composed mainly of olivine and pyroxene.


22

• Extrusive igneous rocks are those that cool from lava that has erupted at Earth’s surface.

Extrusive Igneous Rocks

• These rocks may have the same compositions as intrusive igneous rocks, but they always will have different textures.

• Composition of the surrounding rock material will also affect the extrusive magma.


22

• A magma rich in silica (SiO2) forms rhyolite if it cools rapidly.

Extrusive Igneous Rock Composition

• Similarly, gabbro’s fine-grained volcanic counterpart is basalt, which is a common rock in Earth’s oceanic crust.


22 Extrusive Igneous Rock Composition


22

• If cooling starts off slowly below the surface with large crystals, but then finishes at a faster rate to form small or no crystals, the extrusive rock is called porphyry.

Extrusive Igneous Rock Textures


22

• A texture called vesicular forms near the top surface of a flow where gases escape.

Effect of Gases

22Question 1

What might you expect to find if you examined a rock under a microscope?


Answer

A rock is a naturally formed consolidated mixture containing minerals, rock fragments, or volcanic glass.

22Question 2

Igneous rocks form from molten rock material called _______.

A. basaltB. silicaC. magmaD. granite


22Answer

The answer is C. There are two types of igneous rocks; intrusive and extrusive.


22Question 3

Extrusive igneous rocks form when _______ cools.

A. lavaB. magmaC. waterD. volcanic glass


22Answer

The answer is B. When magma reaches Earth’s surface it is called lava.


Rocks From Surface Materials

• Rocks inside Earth are protected from surface conditions.

• Rock exposed at the surface is attacked by the weather.

Sedimentary RocksSedimentary Rocks

33

• Rock is a consolidated mixture of minerals. Some of these minerals could be in bits and pieces of other rocks. Such small bits and pieces are called clasts.

• When clasts are loose on Earth’s surface, they don’t fit together perfectly. The empty space in between the grains is called porosity.

Transportation and Deposition• Mechanical weathering processes break

into smaller clasts.• When clasts are transported

to new locations, they often become rounded before being deposited.


33

Transportation and Deposition

• When buried by more sediment deposited above them, clasts can be smashed together with such great force that they become compressed and stick together.


33

• This process is called compaction.

• Most of the time both compaction and cementation work together to make sedimentary rock.

Transportation and Deposition• Water moving between clasts carries dissolved

minerals that can act as cement. This process is called cementation.


33

Detrital Sedimentary Rock

• Detritus is another name given to clasts.


33

• Clasts can come in many sizes.

• In order of decreasing size, clasts are known as gravel, sand, silt, or clay.

Detrital Sedimentary Rock• Geologists have found

that size works well as a clue to the kind of environment in which a rock formed.


33

• It takes more force, or energy, to lift or move gravel than it does to lift or move sand.

Detrital Sedimentary Rock


33

• Detrital sedimentary rock composition depends on sources to rock material that were eroded, transported, and eventually deposited.

Detrital Sedimentary Rock• Some minerals tend to be more common

in detrital sediments because they are harder or more resistant to being dissolved.


33

• Geologists examine sedimentary rock compositions and try to reconstruct what happened to form them.

• The general rock name is determined by the clast size.

• Clast size also provides clues to help determine the deposition environment of the sediment that formed the detrital rock.


33 Detrital Sedimentary Rock

Chemical Sedimentary Rocks

• If water receives more dissolved materials than it can hold in solution, then the excess must precipitate out as microscopic crystals.


33

Precipitation

Evaporation• The other option is for some water to evaporate.

• This leaves an oversupply of dissolved matter and again crystals.

Biochemical Sedimentary Rocks

• If sedimentary rocks contain the remains of living organisms they are called biochemical sedimentary rocks.


33

• Limestone is composed, of the remains of marine organisms that had hard parts made of calcium carbonate.

• Coal is sedimentary rock composed almost entirely of the carbon that remains after plant material is compressed underground.

Biochemical Sedimentary Rocks

• Coal goes through a series of changes as it forms from peat.


33

• Each stage of compaction drives out more impurities and leaves behind a more concentrated form of carbon.


Question 1

Small bits and pieces of rock are called _______.

A. clastsB. fragmentsC. pebblesD. pieces

33


Answer

The answer is A. The word clast is from the Greek klastos which means “broken.”

33


Question 2

Which is NOT a type of clast?

A. clayB. gravelC. sedimentD. silt

33


Answer

The answer is C. The four types of clasts are gravel, sand, silt, and clay. Sediment can contain any of these types of clasts.

33


Question 3

_______ is a type of biochemical sedimentary rock that humans use to make electricity.

33

A. CoalB. LimestoneC. GypsumD. Quartz


Answer

The answer is A. Coal is composed almost entirely of carbon.

33

Metamorphic Rocks

• Metamorphic rocks, have been changed by some combination of thermal energy, pressure, and chemical activity.

• Any igneous, sedimentary, or metamorphic rock is subject to change through metamorphism.

Metamorphic Rocks and the Rock CycleMetamorphic Rocks and the Rock Cycle

44

Metamorphic Rock Composition

• Clay minerals tend to form micas with increasing metamorphic conditions.

• Some new minerals form by dehydration at higher temperature and pressure.

44

Changing Minerals


Changing Minerals

• Deep burial or regional movements of large parts of Earth’s crust and uppermost mantle cause regional metamorphism.

• Local contact of any preexisting rock with magma is called contact metamorphism.

44Metamorphic Rocks and the Rock CycleMetamorphic Rocks and the Rock Cycle

• Foliated textures in metamorphic rocks have lots of layers or bands.

• Nonfoliated metamorphic textures include rocks whose grains are in more random orientations.

44 Changing Minerals


Foliated Rocks• The most common sedimentary rocks

in Earth’s crust are mudrocks.• These

rocks contain abundant clay minerals.


Foliated Rocks

• Nonfoliated metamorphic rocks tend to have random crystal orientation and uniform grain size.

• Mineral grains tend to grow as the grade of metamorphism increases.


Metamorphic Rock Classification

• Much like other rock types, metamorphic rocks can be classified based on texture and composition.


Metamorphic Rock Classification

• Mineral composition provides clues about the original rock type before metamorphism, and indicates to what degree a rock had been metamorphosed.


The Rock Cycle

• Processes of the rock cycle include any chemical and physical conditions that continuously form and change rocks.



Question 1

Which is NOT an agent of metamorphism?

A. chemical activityB. pressureC. thermal energyD. wind

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Answer

The answer is D. Wind is responsible for erosion on some rocks but it does not help form them.

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Question 2

Describe foliated metamorphic rocks.

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Answer

Foliated textures in metamorphic rocks have lots of layers or bands in them.

44


Question 3

Is there a beginning and end to the rock cycle?

Answer

No, the rock cycle is a continual process in which rocks change from one form to another.

44

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chapter: earth materials table of contents section 2: igneous rocksigneous rocks section 1: minerals...

Documents

minerals section

streak minerals

minerals structure

metallic luster minerals

common elements minerals

hardness slide

mineral breaks

color of mineral