Download 2 Rocks and Processes of the Rock Cycle

Geology
Steven Kekelik
Dana Desonie, Ph.D.
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AUTHORS
Steven Kekelik
Dana Desonie, Ph.D.
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Printed: August 30, 2013
iii
Contents
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Contents
1
Rocks
1
2
Rocks and Processes of the Rock Cycle
7
3
Igneous Rocks
11
4
Sedimentary Rocks
15
5
Metamorphic Rocks
18
6
Materials Humans Use
21
7
Finding and Mining Ores
24
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C HAPTER
Chapter 1. Rocks
1
Rocks
• Define rock.
How many different rock types are in this photo?
A beach or river bed is a good place to see a lot of different rock types since the rocks there represent the entire
drainage system. How could you tell how many different rock types were in the photo? What characteristics would
you look for?
What Are Rocks?
A rock is a naturally formed, non-living Earth material. Rocks are made of collections of mineral grains that are
held together in a firm, solid mass (Figure 1.1).
How is a rock different from a mineral? Rocks are made of minerals. The mineral grains in a rock may be so tiny
that you can only see them with a microscope, or they may be as big as your fingernail or even your finger (Figure
1.2).
Rocks are identified primarily by the minerals they contain and by their texture. Each type of rock has a distinctive
set of minerals. A rock may be made of grains of all one mineral type, such as quartzite. Much more commonly,
rocks are made of a mixture of different minerals. Texture is a description of the size, shape, and arrangement of
mineral grains. Are the two samples in Figure 1.3 the same rock type? Do they have the same minerals? The same
texture?
TABLE 1.1: Properties of Sample 1 and Sample 2
Sample
Sample 1
Minerals
plagioclase,
hornblende,
pyroxene
Texture
Crystals, visible to
naked eye
Formation
Magma
cooled
slowly
Rock type
Diorite
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TABLE 1.1: (continued)
Sample
Sample 2
2
Minerals
plagioclase,
hornblende,
pyroxene
Texture
One type of crystal
visible, rest microscopic
Formation
Magma erupted and
cooled quickly
Rock type
Andesite
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Chapter 1. Rocks
FIGURE 1.1
The different colors and textures seen in
this rock are caused by the presence of
different minerals.
FIGURE 1.2
A pegmatite from South Dakota with crystals of lepidolite, tourmaline, and quartz (1
cm scale on the upper left).
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FIGURE 1.3
Rock samples.
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Chapter 1. Rocks
As seen in Table 1.1, these two rocks have the same chemical composition and contain mostly the same minerals,
but they do not have the same texture. Sample 1 has visible mineral grains, but Sample 2 has some visible grains in
a fine matrix. The two different textures indicate different histories. Sample 1 is a diorite, a rock that cooled slowly
from magma (molten rock) underground. Sample 2 is an andesite, a rock that cooled rapidly from a very similar
magma that erupted onto Earth’s surface.
A few rocks are not made of minerals because the material they are made of does not fit the definition of a mineral.
Coal, for example, is made of organic material, which is not a mineral. Can you think of other rocks that are not
made of minerals?
Summary
• Nearly all rocks are made of minerals. A few are made of materials that do not fit the definition of minerals.
• Rocks are typically identified by the minerals they contain and their textures.
• The texture of a rock describes the size, shape, and arrangement of mineral grains and is a reflection of how
the rock formed.
Making Connections
MEDIA
Click image to the left for more content.
Practice
Use this resource to answer the questions that follow.
MEDIA
Click image to the left for more content.
1. What is a rock?
2. What type of rock is this?
3. What mineral produces the pink pieces?
4. What mineral produces the white pieces?
5. What mineral produces the black pieces?
6. What is a mineral?
Review
1. Name a rock type that is not made of minerals and state how a rock could not be made of minerals.
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2. Can a rock be made of only one type of mineral, or do rocks need to be made of at least two minerals?
3. Why is texture so important in classifying rock types?
References
1. Woudloper. . Public Domain
2. James Stuby (Jstuby). . Public Domain
3. . Rock - Rock samples. Both images under CC-BY-SA 3.0
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C HAPTER
Chapter 2. Rocks and Processes of the Rock Cycle
2
Rocks and Processes of the
Rock Cycle
• Explain the processes of the rock cycle.
Is this what geologists mean by the rock cycle?
Okay, very punny. The rock cycle shows how any type of rock can become any other type of rock. Some rocks may
stay the same type for a long time, for example, if they’re at the base of the crust, but other rocks may relatively
rapidly change from one type to another.
The Rock Cycle
The rock cycle, illustrated in Figure 2.1, depicts how the three major rock types – igneous, sedimentary, and metamorphic - convert from one to another. Arrows connecting the rock types represent the processes that accomplish
these changes.
Rocks change as a result of natural processes that are taking place all the time. Most changes happen very slowly.
Rocks deep within the Earth are right now becoming other types of rocks. Rocks at the surface are lying in place
before they are next exposed to a process that will change them. Even at the surface, we may not notice the changes.
The rock cycle has no beginning or end.
The Three Rock Types
Rocks are classified into three major groups according to how they form. These three types will be described in
more detail in other lessons in this concept, but here is an introduction.
• Igneous rocks form from the cooling and hardening of molten magma in many different environments. The
chemical composition of the magma and the rate at which it cools determine what rock forms. Igneous rocks
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FIGURE 2.1
The Rock Cycle.
can cool slowly beneath the surface or rapidly at the surface. These rocks are identified by their composition
and texture. More than 700 different types of igneous rocks are known.
• Sedimentary rocks form by the compaction and cementing together of sediments, broken pieces of rock-like
gravel, sand, silt, or clay. Those sediments can be formed from the weathering and erosion of preexisting
rocks. Sedimentary rocks also include chemical precipitates, the solid materials left behind after a liquid
evaporates.
• Metamorphic rocks form when the minerals in an existing rock are changed by heat or pressure below the
surface.
A simple explanation of the three rock types and how to identify them can be seen in this video: http://www.youtu
be.com/watch?v=tQUe9C40NEE&feature=fvw.
This video discusses how to identify igneous rocks: http://www.youtube.com/watch?v=Q0XtLjE3siE&feature=c
hannel.
This video discusses how to identify a metamorphic rocks: http://www.youtube.com/watch?v=qs9x_bTCiew&featu
re=related.
The Processes of the Rock Cycle
Several processes can turn one type of rock into another type of rock. The key processes of the rock cycle are
crystallization, erosion and sedimentation, and metamorphism.
Crystallization
Magma cools either underground or on the surface and hardens into an igneous rock. As the magma cools, different
crystals form at different temperatures, undergoing crystallization. For example, the mineral olivine crystallizes out
of magma at much higher temperatures than quartz. The rate of cooling determines how much time the crystals will
have to form. Slow cooling produces larger crystals.
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Chapter 2. Rocks and Processes of the Rock Cycle
Erosion and Sedimentation
Weathering wears rocks at the Earth’s surface down into smaller pieces. The small fragments are called sediments.
Running water, ice, and gravity all transport these sediments from one place to another by erosion. During sedimentation, the sediments are laid down or deposited. In order to form a sedimentary rock, the accumulated sediment
must become compacted and cemented together.
Metamorphism
When a rock is exposed to extreme heat and pressure within the Earth but does not melt, the rock becomes metamorphosed. Metamorphism may change the mineral composition and the texture of the rock. For that reason, a
metamorphic rock may have a new mineral composition and/or texture.
Summary
• The three main rock types are igneous, metamorphic and sedimentary.
• The three processes that change one rock to another are crystallization, metamorphism, and erosion and
sedimentation.
• Any rock can transform into any other rock by passing through one or more of these processes. This creates
the rock cycle.
Making Connections
MEDIA
Click image to the left for more content.
Practice
Use these resources to answer the questions that follow.
This Science Made Fun video discusses the conditions under which the three main rock types form (3c): http://w
ww.youtube.com/watch?v=G7AWGhQynTY&feature=related (3:41).
MEDIA
Click image to the left for more content.
1. How do igneous rocks form?
2. What are the two types of igneous rocks and how do they differ?
3. What are metamorphic rocks?
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4. How do metamorphic rocks form?
5. How do sedimentary rocks form?
6. List three examples of igneous rocks.
7. List three examples of sedimentary rocks.
8. What forms coal?
9. List three examples of metamorphic rocks.
10. Can an igneous rock become an igneous rock? Can a sedimentary rock become a sedimentary rock? Can a
metamorphic rock become a metamorphic rock?
11. Draw an diagram of the rock cycle and include the processes that transform rocks from one type to another.
Review the rock cycle - click a rock to begin.
http://www.phschool.com/atschool/phsciexp/active_art/rock_cycle/index.html
Test your rock identification skills with this activity:
Name that Rock - http://library.thinkquest.org/J002289/rocks.html
Review
1. What processes must a metamorphic rock go through to become an igneous rock?
2. What processes must a sedimentary rock go through to become a metamorphic rock?
3. What types of rocks can become sedimentary rocks and how does that happen?
References
1. Woudloper/Woodwalker; modified by CK-12 Foundation. The Rock Cycle. Public Domain
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C HAPTER
Chapter 3. Igneous Rocks
3
Igneous Rocks
• Describe the factors that determine the composition of igneous rocks.
What makes this landscape so remarkable?
This photo is of the Sierra Nevada Mountains in California. The rocks look so uniform because they are all igneous
intrusive rocks that cooled from a felsic magma to create the granite that you see. Later, the rock was uplifted and
modified by glaciers during the Pleistocene ice ages.
Magma Composition
Different factors play into the composition of a magma and the rock it produces.
Composition of the Original Rock
The rock beneath the Earth’s surface is sometimes heated to high enough temperatures that it melts to create magma.
Different magmas have different composition and contain whatever elements were in the rock or rocks that melted.
Magmas also contain gases. The main elements are the same as the elements found in the crust. Table 3.1 lists the
abundance of elements found in the Earth’s crust and in magma. The remaining 1.5% is made up of many other
elements that are present in tiny quantities.
TABLE 3.1: Elements in Earth’s Crust and Magma
Element
Oxygen
Silicon
Symbol
O
Si
Percent
46.6%
27.7%
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TABLE 3.1: (continued)
Element
Aluminum
Iron
Calcium
Sodium
Potassium
Magnesium
Total
Symbol
Al
Fe
Ca
Na
K
Mg
Percent
8.1%
5.0%
3.6%
2.8%
2.6%
2.1%
98.5%
(Source: http://en.wikipedia.org/wiki/Abundance_of_elements_in_Earth%27s_crust)
How Rocks Melt
Whether rock melts to create magma depends on:
• Temperature: Temperature increases with depth, so melting is more likely to occur at greater depths.
• Pressure: Pressure increases with depth, but increased pressure raises the melting temperature, so melting is
less likely to occur at higher pressures.
• Water: The addition of water changes the melting point of rock. As the amount of water increases, the melting
point decreases.
• Rock composition: Minerals melt at different temperatures, so the temperature must be high enough to melt
at least some minerals in the rock. The first mineral to melt from a rock will be quartz (if present) and the last
will be olivine (if present).
The different geologic settings that produce varying conditions under which rocks melt will be discussed in Concept
Plate Tectonics.
What Melts and What Crystallizes
As a rock heats up, the minerals that melt at the lowest temperatures melt first. Partial melting occurs when the
temperature on a rock is high enough to melt only some of the minerals in the rock. The minerals that will melt will
be those that melt at lower temperatures. Fractional crystallization is the opposite of partial melting. This process
describes the crystallization of different minerals as magma cools.
Here’s a fractional crystallization animation: http://authors.ck12.org/wiki/images/d/df/Fractional_Crystallization.
swf.
Bowen’s Reaction Series indicates the temperatures at which minerals melt or crystallize (Figure 3.1). An understanding of the way atoms join together to form minerals leads to an understanding of how different igneous rocks
form. Bowen’s Reaction Series also explains why some minerals are always found together and some are never
found together.
To see a diagram illustrating Bowen’s Reaction Series, visit this website: http://csmres.jmu.edu/geollab/Fichter/Ro
ckMin/RockMin.html.
This excellent video that explains Bowen’s Reaction Series in detail: http://www.youtube.com/watch?v=en6ihAM9f
e8.
If the liquid separates from the solids at any time in partial melting or fractional crystallization, the chemical
composition of the liquid and solid will be different. When that liquid crystallizes, the resulting igneous rock will
have a different composition from the parent rock.
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Chapter 3. Igneous Rocks
FIGURE 3.1
Bowen’s Reaction Series.
Summary
• Melting of an existing rock to create magma depends on that rock’s composition and on the temperature,
pressure, and water content found in that environment.
• Bowen’s Reaction Series indicates the temperatures at which minerals crystallize from a magma or melt from
a rock.
• Since minerals melt at different temperatures, a rock in which some minerals have melted has undergone
partial melting; the opposite process, in which some minerals crystallize out of a magma, is fractional crystallization.
Practice
Use this resource to answer the questions that follow.
Geology: Igneous Rocks
http://www.videojug.com/film/geology-igneous-rocks
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MEDIA
Click image to the left for more content.
1. How is igneous rock formed?
2. How does crystallization occur?
3. Explain how extrusive igneous rock is formed.
4. Explain how intrusive igneous rock is formed.
5. What is pyroclastic rock?
6. How are pyroclastic rocks formed?
Review
1. Why are olivine and quartz never found together in an igneous rock?
2. How do changes in temperature, pressure, and fluids cause melting?
3. Briefly describe what Bowen’s Reaction Series depicts.
References
1. CK-12 Foundation. . CC-BY-NC-SA 3.0
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C HAPTER
Chapter 4. Sedimentary Rocks
4
Sedimentary Rocks
• Describe factors that determine the composition of sedimentary rocks.
What is this material and what created the ripples?
If you’ve walked on a sandy beach or on a sand dune, you may have seen ripples like this formed from wind or
waves. Sand is small broken pieces of rock that can be moved around. They can also be lithified to become a rock
known as sandstone.
Sediments
Sandstone is one of the common types of sedimentary rocks that form from sediments. There are many other types.
Sediments may include:
• fragments of other rocks that often have been worn down into small pieces, such as sand, silt, or clay.
• organic materials, or the remains of once-living organisms.
• chemical precipitates, which are materials that get left behind after the water evaporates from a solution.
Rocks at the surface undergo mechanical and chemical weathering. These physical and chemical processes break
rock into smaller pieces. Mechanical weathering simply breaks the rocks apart. Chemical weathering dissolves
the less stable minerals. These original elements of the minerals end up in solution and new minerals may form.
Sediments are removed and transported by water, wind, ice, or gravity in a process called erosion (Figure 4.1).
Much more information about weathering and erosion can be found in Concept Surface Processes and Landforms.
Streams carry huge amounts of sediment (Figure 4.2). The more energy the water has, the larger the particle it can
carry. A rushing river on a steep slope might be able to carry boulders. As this stream slows down, it no longer has
the energy to carry large sediments and will drop them. A slower moving stream will only carry smaller particles.
Sediments are deposited on beaches and deserts, at the bottom of oceans, and in lakes, ponds, rivers, marshes, and
swamps. Landslides drop large piles of sediment. Glaciers leave large piles of sediments, too. Wind can only
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FIGURE 4.1
Water erodes the land surface in Alaska’s Valley of Ten Thousand Smokes
FIGURE 4.2
A river dumps sediments along its bed
and on its banks.
transport sand and smaller particles. The type of sediment that is deposited will determine the type of sedimentary
rock that can form. Different colors of sedimentary rock are determined by the environment where they are deposited.
Red rocks form where oxygen is present. Darker sediments form when the environment is oxygen poor.
Summary
• Rocks undergo chemical or mechanical weathering to form smaller pieces.
• Sediments range in size from tiny bits of silt or clay to enormous boulders.
• Sediments are transported by wind, water, ice, or gravity into different environments.
Practice
Use these resources to answer the questions that follow.
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Chapter 4. Sedimentary Rocks
http://www.windows2universe.org/earth/geology/sed_intro.html
1. What percentage of rocks are sedimentary?
2. Where are sedimentary rocks found?
3. What can scientists learn from sedimentary rocks?
4. List and explain each of the types of sedimentary rocks?
http://www.windows2universe.org/earth/geology/sed_clastic.html
5. How is clastic sedimentary rock formed?
6. What holds the sediment together?
7. What is Cathedral Rocked made of?
Review
1. What does sediment size indicate about the history of that sediment?
2. How are chemical precipitates different from rocks that form from sediment particles?
3. Why are organic materials considered sediments but not minerals?
References
1. Courtesy of the National Oceanic and Atmospheric Administration. Alaska’s Valley of Ten Thousand Smokes.
Public Domain
2. ZackClark. . Public Domain
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C HAPTER
5
Metamorphic Rocks
• Explain how metamorphic rocks form.
Can you decipher the history of this rock?
The rock in this photo is a banded gneiss. The bands are of different composition, more felsic and more mafic, that
separated as a result of heat and pressure. The waviness of the bands also shows how the rock was hot enough to
alter but not to melt all the way.
Metamorphism
Any type of rock – igneous, sedimentary, or metamorphic — can become a metamorphic rock. All that is needed
is enough heat and/or pressure to alter the existing rock’s physical or chemical makeup without melting the rock
entirely. Rocks change during metamorphism because the minerals need to be stable under the new temperature and
pressure conditions. The need for stability may cause the structure of minerals to rearrange and form new minerals.
Ions may move between minerals to create minerals of different chemical composition. Hornfels, with its alternating
bands of dark and light crystals, is a good example of how minerals rearrange themselves during metamorphism.
Hornfels is shown in Table in "Metamorphic Rock Classification."
Texture
Extreme pressure may also lead to foliation, the flat layers that form in rocks as the rocks are squeezed by pressure
(Figure 5.1). Foliation normally forms when pressure is exerted in only one direction. Metamorphic rocks may also
be non-foliated. Quartzite and limestone, shown in Table below, are non-foliated.
Types of Metamorphism
The two main types of metamorphism are both related to heat within Earth:
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Chapter 5. Metamorphic Rocks
FIGURE 5.1
A foliated metamorphic rock.
1. Regional metamorphism: Changes in enormous quantities of rock over a wide area caused by the extreme
pressure from overlying rock or from compression caused by geologic processes. Deep burial exposes the
rock to high temperatures.
2. Contact metamorphism: Changes in a rock that is in contact with magma. The changes occur because of the
magma’s extreme heat.
Summary
• Any type of rock - igneous, sedimentary or metamorphic - can become a metamorphic rock.
• Foliated rocks form when rocks being metamorphosed are exposed to pressure in one direction.
• Regional metamorphism occurs over a large area but contact metamorphism occurs when a rock is altered by
a nearby magma.
Practice
Use this resource to answer the questions that follow.
http://library.thinkquest.org/J002289/meta.html
1. How do metamorphic rocks form?
2. Where does the heat come from to change these rocks?
3. What produces the pressure to change these rocks?
4. List the characteristics of metamorphic rocks.
5. List examples of metamorphic rocks.
Review
1. Why do changes in temperature or pressure cause rocks to change?
2. What are the similarities and differences in conditions that cause regional versus contact metamorphism?
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3. What causes foliation in a metamorphic rock? Under what circumstances would you expect this to happen?
References
1. . A foliated metamorphic rock. CC-BY-SA 3.0
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C HAPTER
Chapter 6. Materials Humans Use
6
Materials Humans Use
• Identify resources commonly consumed by human uses.
What resources are in those electronics?
Everyone may realize that we use resources like trees, copper, water, and gemstones, but how many of us realize the
tremendous variety of elements we need to make a single electronic device? A tablet computer with a touch screen
contains many common chemical elements and a variety of rare earth elements.
Common Materials We Use from the Earth
People depend on natural resources for just about everything that keeps us fed and sheltered, as well as for the things
that keep us entertained. Every person in the United States uses about 20,000 kilograms (40,000 pounds) of minerals
every year for a wide range of products, such as cell phones, TVs, jewelry, and cars. Table 6.1 shows some common
objects, the materials they are made from, and whether they are renewable or nonrenewable.
TABLE 6.1: Common Objects We Use From the Earth
Common Object
Natural Resources Used
Cars
15 different metals, such as iron,
lead, and chromium to make the
body.
Precious metals like gold, silver,
and platinum.
Gems like diamonds, rubies, emeralds, turquoise.
Many different metals, like copper,
mercury, gold.
Jewelry
Electronic Appliances (TV’s, computers, DVD players, cell phones,
etc.)
Are These Resources Renewable or
Nonrenewable?
Nonrenewable
Nonrenewable
Nonrenewable
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TABLE 6.1: (continued)
Common Object
Natural Resources Used
Clothing
Soil to grow fibers such as cotton.
Sunlight for the plants to grow.
Animals for fur and leather.
Soil to grow plants.
Wildlife and agricultural animals.
Water from streams or springs.
Petroleum products to make plastic
bottles.
Petroleum drilled from wells.
Coal, natural gas, solar power, wind
power, hydroelectric power.
Trees; Sunlight Soil.
Trees for timber.
Rocks and minerals for construction materials, for example, granite,
gravel, sand.
Food
Bottled Water
Gasoline
Household Electricity
Paper
Houses
Are These Resources Renewable or
Nonrenewable?
Renewable
Renewable
Nonrenewable and Renewable
Nonrenewable
Nonrenewable and Renewable
Renewable
Nonrenewable and Renewable
Summary
• Many objects, such as a car, contain many types of resources.
• Resources may be renewable or nonrenewable, and an object may contain some of each.
• Rare earth elements and other unusual materials are used in some electronic devices.
Practice
Use this resource to answer the questions that follow.
http://www.bbc.co.uk/news/world-asia-pacific-13777439
1. What products require rare earth elements?
2. What is neodymium used for?
3. What is lanthanum used for?
4. What is praseodymium used for?
5, What is cerium used to produce?
6. What is gadolinium used in?
7. What country controls 97% of the rare earth elements?
8. What is the largest rare earth mine in the world?
9. Why are rare earth elements difficult to extract?
10. What type of mines are used to extract rare earth elements?
11. How many tons of rare earth elements did China export in 2010?
12. Why is China now limiting their exports?
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Chapter 6. Materials Humans Use
Review
1. What resources are important to you that are renewable? Nonrenewable?
2. What resources do you use that you could use less or not use at all?
3. How might one of these resources go from being renewable to nonrenewable?
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C HAPTER
7
Finding and Mining Ores
• Describe how ore deposits are located, mined, and refined to become useful materials.
Why is the football team in San Francisco named the 49ers?
Football team names sometimes reflect the history of a region. The San Francisco 49ers are a reference to the
California Gold Rush, when immigrants from around the United States came to what would become The Golden
State to mine placer deposits. What that has to do with football is anyone’s guess!
Ore Deposits
Some minerals are very useful. An ore is a rock that contains minerals with useful elements. Aluminum in bauxite
ore (Figure 7.1) is extracted from the ground and refined to be used in aluminum foil and many other products. The
cost of creating a product from a mineral depends on how abundant the mineral is and how much the extraction and
refining processes cost. Environmental damage from these processes is often not figured into a product’s cost. It is
important to use mineral resources wisely.
Finding and Mining Minerals
Geologic processes create and concentrate minerals that are valuable natural resources. Geologists study geological
formations and then test the physical and chemical properties of soil and rocks to locate possible ores and determine
their size and concentration.
A mineral deposit will only be mined if it is profitable. A concentration of minerals is only called an ore deposit if
it is profitable to mine. There are many ways to mine ores.
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Chapter 7. Finding and Mining Ores
FIGURE 7.1
Aluminum is made from the aluminumbearing minerals in bauxite.
Surface Mining
Surface mining allows extraction of ores that are close to Earth’s surface. Overlying rock is blasted and the rock that
contains the valuable minerals is placed in a truck and taken to a refinery. As pictured in Figure 7.2, surface mining
includes open-pit mining and mountaintop removal. Other methods of surface mining include strip mining, placer
mining, and dredging. Strip mining is like open pit mining but with material removed along a strip.
FIGURE 7.2
These different forms of surface mining are methods of extracting ores close to Earth’s surface.
Placers are valuable minerals found in stream gravels. California’s nickname, the Golden State, can be traced back
to the discovery of placer deposits of gold in 1848. The gold weathered out of hard metamorphic rock in the western
Sierra Nevada, which also contains deposits of copper, lead, zinc, silver, chromite, and other valuable minerals. The
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gold traveled down rivers and then settled in gravel deposits. Currently, California has active mines for gold and
silver and for non-metal minerals such as sand and gravel, which are used for construction.
Underground Mining
Underground mining is used to recover ores that are deeper into Earth’s surface. Miners blast and tunnel into rock
to gain access to the ores. How underground mining is approached — from above, below, or sideways — depends
on the placement of the ore body, its depth, the concentration of ore, and the strength of the surrounding rock.
Underground mining is very expensive and dangerous. Fresh air and lights must also be brought into the tunnels for
the miners, and accidents are far too common.
FIGURE 7.3
Underground mine.
Ore Extraction
The ore’s journey to becoming a useable material is only just beginning when the ore leaves the mine (Figure
7.4). Rocks are crushed so that the valuable minerals can be separated from the waste rock. Then the minerals are
separated out of the ore. A few methods for extracting ore are:
• heap leaching: the addition of chemicals, such as cyanide or acid, to remove ore.
• flotation: the addition of a compound that attaches to the valuable mineral and floats.
• smelting: roasting rock, causing it to segregate into layers so the mineral can be extracted.
To extract the metal from the ore, the rock is melted at a temperature greater than 900o C, which requires a lot of
energy. Extracting metal from rock is so energy-intensive that if you recycle just 40 aluminum cans, you will save
the energy equivalent of one gallon of gasoline.
Summary
• An ore deposit must be profitable to mine by definition. If it is no longer profitable, it is no longer an ore
deposit.
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Chapter 7. Finding and Mining Ores
FIGURE 7.4
Enormous trucks haul rock containing ore
from a mine site to where the rock is
processed.
FIGURE 7.5
A steel mill.
• Surface mines are created for mineral deposits that are near the surface; underground mines are blasted into
rock to get at deeper deposits.
• Ore is extracted from rock by heap leaching, flotation or smelting.
Practice
Use this resource to answer the questions that follow.
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MEDIA
Click image to the left for more content.
1. What is the Superpit?
2. How large is the Superpit?
3. How is gold extracted from this mine?
4. What is Australia’s rank in gold mining?
5. What minerals is Australia the leading country for?
Review
1. What sorts of changes can transform a deposit that is an ore into a deposit that is not an ore?
2. Why is the production of the metal to create your aluminum soda can energy-intensive?
3. How is ore taken from a rock and made into a metal like a copper wire?
References
1. Courtesy of US Geological Survey/Mineral Information Institute. . Public Domain
2. (a) Eric Guinther (Marshman); (b) Courtesy of Jesse Allen/NASA’s Earth Observatory; (c) iLoveMountains.org; Composite created by CK-12 Foundation. Surface mining. (a) CC-BY-SA 3.0; (b) Public Domain;
(c) CC-BY 2.0
3. . . CC-BY-SA 3.0
4. Nick Bonzey. . CC-BY-SA 2.0
5. Třinecké železárny. . The copyright holder of this file allows anyone to use it for any purpose provided that
the copyright holder is properly attributed.
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