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CHAPTER 5
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Minerals of Earth’s Crust
1 What Is a Mineral?
SECTION
KEY IDEAS
As you read this section, keep these questions in mind:
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•
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What is a mineral?
What are the two main groups of minerals?
What are the six types of silicate crystal structures?
What are three nonsilicate crystal structures?
What Is a Mineral?
A gold nugget, a grain of road salt, and a ruby may
seem very different, but they have one thing in common:
they are all minerals. A mineral has these properties:
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It forms naturally.
It is not made by living things.
It is solid.
Its atoms and molecules are arranged in a pattern.
READING TOOLBOX
Make Connections As you
read, make flash cards for
the highlighted terms in this
section. Add any other terms
you think are important. After
you read, work with a partner
to practice using each term
correctly in a sentence.
It is made up of certain elements combined in specific
ratios.
• It has specific physical properties.
All minerals form naturally. In other words, people do
not make them. Therefore, steel is not a mineral, because
people make it.
Organic matter is matter that is found in living things,
or that is made by living things. Inorganic matter is matter that is not made by living things. All minerals are
inorganic. For example, coal is not a mineral, because it
forms from the remains of plants.
The atoms and molecules in a solid mineral are
arranged in a pattern. This arrangement causes the mineral to form crystals. A crystal is a solid with a regular
arrangement of atoms or molecules. Crystals generally
have geometric shapes, such as cubes.
Every sample of a mineral is made up of the same elements. For example, every sample of the mineral quartz
is made up mainly of the elements silicon and oxygen.
Those elements are combined in a ratio of 1:2 (SiO2).
Scientists describe this property of minerals by saying
that minerals have a consistent chemical composition.
READING CHECK
1. Explain Why is steel not a
mineral?
Critical Thinking
2. Apply Concepts Glass is
made up of silicon and oxygen atoms in a 1:2 ratio. The
SiO2 molecules in glass are
arranged in a random way. Is
glass a mineral? Explain your
answer.
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What Is a Mineral? continued
Talk About It
Research Use the Internet
or library to find out the
names of the main rockforming minerals. Learn more
about one of the minerals.
Share what you learn with a
partner.
What Are the Two Main Kinds of Minerals?
There are thousands of different minerals. However,
only about 20 minerals are common on Earth. These
20 common minerals are called rock-forming minerals
because they make up most rocks on Earth.
Scientists divide minerals into two main groups based
on their chemical compositions. The two groups are silicate minerals and nonsilicate minerals.
SILICATE MINERALS
READING CHECK
3. List What two elements
do all silicate minerals contain?
Most minerals on Earth are silicate minerals.
A silicate mineral contains combinations of silicon (Si)
and oxygen (O) atoms. Quartz, feldspars, micas, and olivine are examples of silicate minerals.
Quartz is made up of silicon and oxygen. All other silicate minerals also contain other elements. For example,
feldspars contain sodium, calcium, or potassium in addition to silicon and oxygen. Olivine contains magnesium,
iron, silicon, and oxygen.
NONSILICATE MINERALS
Only about 4% of Earth’s crust is made of nonsilicate
minerals. A nonsilicate mineral does not contain combinations of silicon and oxygen. It may contain silicon or
oxygen, but they are not bonded together.
There are six main groups of nonsilicate minerals. The
table below describes these six groups.
LOOKING CLOSER
4. Compare Which element
is found in all sulfate minerals, but not in sulfide minerals?
Type of
Nonsilicate
Mineral
Description
Examples
Carbonates
contain a carbonate group
(CO3)
dolomite, CaMg(CO3)2;
calcite, CaCO3
Halides
contain chlorine or fluorine
combined with sodium,
potassium, or calcium
fluorite, CaF2; halite, NaCl
Native
elements
made of atoms of a single
element
silver, Ag; copper, Cu
Oxides
contain oxygen and an
element other than silicon
corundum, Al2O3; hematite,
Fe2O3
Sulfates
contain a sulfate group (SO4)
anhydrite, CaSO4
Sulfides
contain sulfur combined with galena, PbS; pyrite, FeS2
another element (a metal)
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What Is a Mineral? continued
What Types of Crystals Do Minerals Form?
The atoms and molecules in different minerals are
arranged in different patterns. The arrangement of the
atoms and molecules affects the shape of the crystals the
mineral forms.
One way scientists identify minerals is by studying
their crystal shapes. The atoms and molecules in a mineral are always arranged the same way. Therefore, a mineral always forms the same crystal shape.
CRYSTALLINE STRUCTURE OF SILICATE MINERALS
There are many different kinds of silicate minerals.
They form many different kinds of crystals. However,
the crystals of all silicate minerals have similar building
blocks.
The building blocks of silicate minerals are made of
atoms of silicon and oxygen. Each building block
contains one silicon atom and four oxygen atoms. The
oxygen atoms form a pyramid. The silicon atom is in
the center of the pyramid. This structure is called a
silicon-oxygen tetrahedron.
Oxygen
Silicon
READING CHECK
5. Explain Why does a mineral always form crystals with
the same shape?
Talk About It
Make Connections Use a
dictionary to look up the
meaning of the word
tetrahedron. With a partner,
discuss why the building
blocks of silicate minerals
are called silicon-oxygen
tetrahedrons.
Oxygen
Silicon
These drawings show two different models of a silicon-oxygen tetrahedron.
Silicon-oxygen tetrahedrons are arranged in different
ways in different silicate minerals. There are two factors
that affect how the tetrahedrons are arranged. First, the
tetrahedrons may form bonds with atoms of other elements, such as potassium or magnesium. Those bonds
change the way the tetrahedrons are arranged.
Second, the tetrahedrons may share oxygen atoms.
When tetrahedrons share oxygen atoms, they can form
chains, rings, and networks, or webs. The table on the
next page shows how tetrahedrons can share atoms.
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What Is a Mineral? continued
Arrangement
of SiliconOxygen
Tetrahedrons
Description
Examples
Isolated
tetrahedrons
The tetrahedrons in these minerals are
not linked to other silicon or oxygen
atoms. They may be linked to atoms of
other elements.
olivine
Silicon-oxygen
tetrahedron
LOOKING CLOSER
Rings of
tetrahedrons
The tetrahedrons in these minerals
share oxygen atoms. They form rings
with three, four, or six sides. Atoms of
other elements can also bond to the
rings.
beryl, tourmaline
Single chain of
tetrahedrons
The tetrahedrons in these minerals
share oxygen atoms to form long
chains. Each tetrahedron shares two
oxygen atoms with other tetrahedrons.
pyroxene
Double chain
of tetrahedrons
amphibole
These minerals have double chains of
tetrahedrons. The double chains form
when two single chains join together by
sharing oxygen atoms.
Sheets of
tetrahedrons
In a sheet of tetrahedrons, each
tetrahedron shares three oxygen atoms
with other tetrahedrons.
mica
Framework of
tetrahedrons
Every tetrahedron in these minerals
shares four oxygen atoms with other
tetrahedrons. The tetrahedrons form a
framework, or web.
quartz
6. Identify How are the
silicon-oxygen tetrahedrons
in beryl arranged?
7. Apply Concepts How
many oxygen atoms does
each silicon-oxygen tetrahedron in pyroxene share?
8. Compare Which mineral
listed in the table contains
silicon-oxygen tetrahedrons
that share the most oxygen
atoms with other tetrahedrons?
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What Is a Mineral? continued
GROUPS OF SILICATE MINERALS
There are six main groups of silicate minerals. The
minerals in each group have the same arrangement of
silicon-oxygen tetrahedrons. The names of the groups are
related to the arrangement of the tetrahedrons.
Name of Group
Arrangement of Tetrahedrons
Single-tetrahedron silicates
isolated tetrahedrons
Ring silicates
rings of tetrahedrons
Single-chain silicates
single chains of tetrahedrons
Double-chain silicates
double chains of tetrahedrons
Sheet silicates
sheets of tetrahedrons
Framework silicates
frameworks of tetrahedrons
LOOKING CLOSER
9. List What are the six main
groups of silicate minerals?
CRYSTAL STRUCTURES OF NONSILICATE MINERALS
Remember that there are many different kinds of
nonsilicate minerals. Each nonsilicate mineral contains
different atoms and molecules. The atoms and molecules
in nonsilicate minerals can be arranged in many different
ways. Therefore, nonsilicate minerals can have a variety
of crystal shapes. The three most common crystal
structures for nonsilicate minerals are cubes, hexagonal
(six-sided) prisms, and irregular shapes.
Some nonsilicate minerals have similar arrangements
of atoms and molecules. These minerals also have similar
crystal structures. For example, many halide and sulfide
minerals form cubes, because their atoms and molecules
are arranged in similar ways.
LOOKING CLOSER
10. Explain Why do galena
and halite form crystals with
similar shapes?
Galena, a sulfide mineral
Halite, a halide mineral
Halite and galena both form cubic crystals. They form crystals with similar shapes
because the atoms in the minerals are arranged in a similar way.
The arrangement of atoms and molecules in a crystal affects the mineral’s properties. For example, many
native elements are very dense. They are dense because
the atoms in them are packed very close together.
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Section 1 Review
SECTION VOCABULARY
crystal a solid whose atoms, ions, or molecules
are arranged in a regular, repeating pattern
mineral a natural, usually inorganic solid that
has a characteristic chemical composition, an
orderly internal structure, and a characteristic
set of physical properties
nonsilicate mineral a mineral that does not
contain compounds of silicon and oxygen
silicate mineral a mineral that contains a combination of silicon and oxygen and that may
also contain one or more metals
silicon-oxygen tetrahedron the basic unit of
the structure of silicate minerals; a silicon ion
chemically bonded to and surrounded by four
oxygen ions
1. Compare What is the difference between silicate minerals and nonsilicate miner-
als?
2. Identify What are the three most common nonsilicate crystal structures?
3. Apply Concepts Give one example of a mineral. Describe at least three character-
istics that show that it is a mineral.
4. Infer An Earth scientist discovers a new mineral. The mineral is made up of gold
and sulfur atoms bonded together. Which group of nonsilicate mineral does this
mineral belong in?
5. Compare Quartz is a framework silicate. Pyroxene is a single-chain silicate.
Describe how these two minerals are different and how they are similar.
6. Explain Corundum (Al2O3) and hematite (Fe2O3) both contain oxygen, but they
are not considered to be silicate minerals. Why is this?
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