Download What Is a Mineral?

1
What Is a Mineral?
1
Overview
READI NG WARM-U P
This section explores the nature
of minerals by describing their
four characteristics. Students
learn that mineral crystals are
generated by atomic structures,
and they learn how to classify
minerals into two major compositional groups—silicates
and nonsilicates.
Objectives
•
•
Bellringer
Mineral Structure
mineral
element
compound
crystal
silicate mineral
nonsilicate mineral
By answering the four questions in Figure 1, you can tell
whether an object is a mineral. If you cannot answer “yes” to
all four questions, you don’t have a mineral. Three of the four
questions may be easy to answer. The question about crystalline
structure may be more difficult. To understand what crystalline
structure is, you need to know a little about the elements that
make up a mineral. Elements are pure substances that cannot
be broken down into simpler substances by ordinary chemical
means. All minerals contain one or more of the 92 naturally
occurring elements.
Paired Summarizing Read this section
silently. In pairs, take turns summarizing the material. Stop to discuss ideas
that seem confusing.
Is it nonliving
material?
A mineral is inorganic,
meaning it isn’t made
of living things.
Is it a solid?
Minerals can’t
be gases
or liquids.
v -------g
Identifying Minerals Place an
assortment of objects on a table.
Possibilities include a piece of
wood, a fossil, a piece of bone,
a piece of granite, and a quartz
crystal. Organize the class into
groups of two or three students.
Tell the students to examine the
objects and to determine which
ones are minerals by using the
four questions in Figure 1 on
this page. l Logical/Verbal
Does it have a
crystalline structure?
Minerals are crystals, which
have a repeating inner structure
that is often reflected in the
shape of the crystal. Minerals
generally have the same chemical composition throughout.
Is it formed
in nature?
Crystalline materials
made by people
aren’t classified as
minerals.
Figure 1 The answers to these
four questions will determine
whether an object is a mineral.
CHAPTER RESOURCES
Chapter Resource File
CRF
• Lesson Plan
• Directed Reading A b
• Directed Reading B s
Technology
Transparencies
• Bellringer
66
For one thing, rocks are made of minerals, but minerals are
not made of rocks. A mineral is a naturally formed, inorganic
solid that has a definite crystalline structure.
Terms to Learn
READI NG STRATEGY
Display a piece of pencil lead
(graphite) and a photograph of a
diamond. Explain that both substances are composed of carbon.
Ask students to brainstorm how
two substances with such different properties can form from
atoms of the same element.
Group
Describe the structure of minerals.
Describe the two major groups of
minerals.
You may think that all minerals look like gems. But, in
fact, most minerals look more like rocks. Does this mean
that minerals are the same as rocks? Well, not really. So,
what’s the difference?
Chapter 3 • Minerals of the Earth’s Crust
h -----------------------------g
At Home with Minerals Ask students
to find four items in their home that are
derived from minerals. Have them add
labels to identify the minerals that are
contained in different products. Have students share their findings with the class.
(Examples include table salt, which is composed
of halite; pencil lead, which is composed of
graphite; and cooking pots, which are composed of iron, copper, or aluminum.) l Visual
Atoms and Compounds
Each element is made of only one kind of atom. An
atom is the smallest part of an element that has all the
properties of that element. Like other substances, minerals are made up of atoms of one or more elements.
Most minerals are made of compounds of several
different elements. A compound is a substance made of
two or more elements that have been chemically joined,
or bonded. Halite, NaCl, for example, is a compound of
sodium, Na, and chlorine, Cl, as shown in Figure 2. A
few minerals, such as gold and silver, are composed of
only one element. A mineral that is composed of only
one element is called a native element.
Discussion ----------------------------------g
Figure 2 When atoms of sodium
(purple) and chlorine (green) join,
they form a compound commonly
known as rock salt, or the mineral
halite.
Rocks and Minerals Students
may benefit from a discussion
of the differences between rocks
and minerals. Emphasize that
rocks are composed of minerals
but that minerals are not composed of rock. It is possible for a
rock to be made of one mineral
or of many. Minerals should also
not be confused with mineraloids. Mineraloids are similar
to minerals, but mineraloids
have no crystalline structure.
Some common mineraloids
are obsidian, limonite, flint,
and opal. l Verbal
✓
Reading Check How does a compound differ from an
element? (See the Appendix for answers to Reading Checks.)
Crystals
Solid, geometric forms of minerals produced by a repeating pattern of atoms that is present throughout the mineral are called
crystals. A crystal’s shape is determined by the arrangement of
the atoms within the crystal. The arrangement of atoms in
turn is determined by the kinds of atoms that make up the
mineral. Each mineral has a definite crystalline structure. All
minerals can be grouped into crystal classes according to the
kinds of crystals they form. Figure 3 shows how the atomic
structure of gold gives rise to cubic crystals.
Figure 3
Composition of the Mineral Gold
mineral a naturally formed, inorganic solid that has a definite crystalline structure
element a substance that can-
Group
not be separated or broken down
into simpler substances by chemical
means
Mineral Identification
When you begin teaching
this section, give pairs of
students an unknown mineral.
Tell students that their goal will
be to identify the mineral by
the time the class finishes studying the chapter and to present
a short report on the mineral to
the class. Their reports should
include the chemical formula of
the mineral, detail the mineral’s
uses and properties, and explain
how the mineral was formed
and the type of rock in which
the mineral occurs. Student
reports can also include the location of mines where the mineral
is found. l Verbal/Logical
compound a substance made up
of atoms of two or more different elements joined by chemical bonds
crystal a solid whose atoms, ions,
or molecules are arranged in a definite pattern
The mineral gold is composed of gold atoms
arranged in a crystalline structure.
v -------g
Writing
Crystals of the
mineral gold
The atomic
structure of gold
The crystal
structure of gold
Answer to Reading Check
MISCONCEPTION
ALERT
Crystal Form and Mineral Identification
In much the same way that color is a
deceptive guide to identifying minerals,
crystal form is often a misleading
physical property. The unit cells of halite
and gold are shown in Figure 2 and
Figure 3. When different unit cells are
combined, however, they can generate
crystal forms that look nothing like their
atomic structure. A large variety of complex crystal shapes can be generated by
starting with a simple polyhedron, such
as a cube. For example, the mineral fluorite belongs in the isometric (cubic) class
but commonly forms octahedral-shaped
crystals.
An element is a pure substance that
cannot be broken down into simpler
substances by ordinary chemical
means. A compound is a substance
made of two or more elements that
have been chemically bonded.
Section 1 • What Is a Mineral?
67
Two Groups of Minerals
Reteaching -------------------------------------b
Elements and Compounds Have
students prepare a set of cards
for 10 common minerals. Give
students the chemical formula
for each mineral, and have them
write the chemical formula next
to the mineral name. This exercise will reinforce the difference
between minerals that are composed of a single element and
minerals that are composed of
multiple elements. l Visual
Magnetite The
mineral magnetite has a special property—it
is magnetic. Scientists have
found that some animals’
brains contain magnetite. And
scientists have shown that certain fish can sense magnetic
fields because of the magnetite in the brains of these fish.
The magnetite gives the fish a
sense of direction. Using the
Internet or another source,
research other animals that
have magnetite in their brains.
Summarize your findings in a
short essay.
WRITING
SKILL
Quiz ----------------------------------------------------------------------g
1. What is a mineral? (a naturally
formed, inorganic solid that has a
crystalline structure)
Silicon and oxygen are the two most common elements in the
Earth’s crust. Minerals that contain a combination of these two
elements are called silicate minerals. Silicate minerals make up
more than 90% of the Earth’s crust. The rest of the Earth’s crust
is made up of nonsilicate minerals. Silicon and oxygen usually
combine with other elements, such as aluminum, iron, magnesium, and potassium, to make up silicate minerals. Some of
the more common silicate minerals are shown in Figure 4.
Nonsilicate Minerals
Minerals that do not contain a combination of the elements
silicon and oxygen form a group called the nonsilicate minerals.
Some of these minerals are made up of elements such as carbon,
oxygen, fluorine, and sulfur. Figure 5 on the following page
shows the most important classes of nonsilicate minerals.
How do silicate minerals differ from nonsili-
cate minerals?
depend on? (the arrangement of
the atoms within the crystal)
Classifying Minerals Write the
following mineral-group names
on the board: silicates, native
elements, carbonates, halides,
oxides, sulfates, and sulfides. Have
students match the following
items with the mineral group from
which they are derived: a copper
penny (native elements); cement
(carbonates); rock salt (halides);
toothpaste (sulfates); batteries
(sulfides); sand (silicates). l Logical
Silicate Minerals
✓Reading Check
2. What does a crystal’s shape
Alternative
Assessment-----------------------------g
The most common classification of minerals is based on chemical composition. Minerals are divided into two groups based
on their chemical composition. These groups are the silicate
minerals and the nonsilicate minerals.
Figure 4
Common Silicate Minerals
silicate mineral a mineral that
contains a combination of silicon,
oxygen, and one or more metals
Quartz is the basic building
block of many rocks.
nonsilicate mineral a mineral
that does not contain compounds of
silicon and oxygen
Feldspar minerals are
the main component
of most rocks on the
Earth’s surface.
Mica minerals
separate easily into
sheets when they
break. Biotite is one
of several kinds of
mica.
Answer to Reading Check
Answers may vary. Silicate minerals
contain a combination of silicon and
oxygen; nonsilicate minerals do not
contain a combination of silicon and
oxygen.
INCLUSION
Strategies
• Learning Disabilities
• Developmentally Delayed
Organize students into pairs or groups
of three. Give each group some common
mineral samples. Pass out paint sample
strips from a hardware store, and have
students identify each mineral’s color.
Students should record their observations in their science journal. Next,
hand out materials that serve as
68
Chapter 3 • Minerals of the Earth’s Crust
examples of luster. A candle could demonstrate waxy luster, and a jar top is an
example of metallic luster. Have students
use these examples to determine the
luster of each mineral sample. The teams
should perform all of the mineral tests in
a similar way and share their findings
with the class.
l Visual/Kinesthetic
e
Figure 5
Answers to Section Review
Classes of Nonsilicate Minerals
Native elements are minerals
that are composed of only one
element. Some examples are
copper, Cu, gold, Au, and silver,
Ag. Native elements are used in
communications and electronics
Copper
equipment.
Oxides are compounds that
form when an element, such
as aluminum or iron, combines
chemically with oxygen. Oxide
minerals are used to make
abrasives, aircraft parts, and
Corundum
paint.
Carbonates are minerals that
contain combinations of carbon
and oxygen in their chemical
structure. We use carbonate
minerals in cement, building
stones, and fireworks.
Sulfates are minerals that contain sulfur and oxygen, SO4.
Sulfates are used in cosmetics,
toothpaste, cement, and paint.
Halides are compounds that
form when fluorine, chlorine,
iodine, or bromine combine
with sodium, potassium, or
calcium. Halide minerals are
used in the chemical industry
and in detergents.
Review
Summary
mineral is a naturally
• Aformed,
inorganic solid
that has a definite crystalline structure.
Minerals may be either
elements or compounds.
•
crystals are solid,
• Mineral
geometric forms that are
produced by a repeating
pattern of atoms.
are classified
• Minerals
as either silicate minerals or nonsilicate
minerals based on the
elements of which they
are composed.
Calcite
Fluorite
Gypsum
Sulfides are minerals that
contain one or more elements,
such as lead, iron, or nickel,
combined with sulfur. Sulfide
minerals are used to make
batteries, medicines, and
Galena
electronic parts.
Using Key Terms
Critical Thinking
1. In your own words, write a definition for each of the following
terms: element, compound, and
mineral.
Understanding Key Ideas
2. Which of the following minerals
is a nonsilicate mineral?
a.
b.
c.
d.
mica
quartz
gypsum
feldspar
6. Applying Concepts Explain
why each of the following is
not considered a mineral: water,
oxygen, honey, and teeth.
7. Applying Concepts Explain
why scientists consider ice to be
a mineral.
8. Making Comparisons In what
ways are sulfate and sulfide minerals the same. In what ways are
they different?
3. What is a crystal, and what
determines a crystal’s shape?
4. Describe the two major groups
of minerals.
Developed and maintained by the
National Science Teachers Association
Math Skills
5. If there are approximately 3,600
known minerals and about 20 of
the minerals are native elements,
what percentage of all minerals
are native elements?
For a variety of links related to this
chapter, go to www.scilinks.org
Topic: Gems
SciLinks code: HSM0640
CHAPTER RESOURCES
Chapter Resource File
CRF
• Section Quiz g
• Section Review g
• Vocabulary and Section Summary g
• Reinforcement Worksheet b
1. Sample answer: Pure substances that cannot be broken
down into simpler substances
are called elements. Compounds
are two or more elements
bonded together. A mineral is a
naturally formed, inorganic solid
that has a crystalline structure.
2. c
3. A crystal is a solid, geometric
form of mineral produced by a
repeating pattern of atoms that is
present throughout the mineral.
The shape of a crystal is determined by the arrangement of
atoms within the crystal.
4. The two major groups of minerals are silicate and nonsilicate
minerals. Silicate minerals contain a combination of silicon and
oxygen. Nonsilicate minerals do
not contain a combination of silicon and oxygen.
5. 20 3,600 " 100 # .55%
6. Water is not a mineral because
it does not have a crystalline
structure and it is a liquid, not a
solid. Oxygen is not a mineral
because oxygen atoms by themselves do not have a crystalline
structure. Teeth are not minerals
because they are living parts of
your body. Honey is not a mineral
because it is made of organic
substances.
7. Ice is considered to be a mineral
because it is a solid, it is a nonliving material, it is formed in
nature, and it has a definite
crystalline structure.
8. Sulfate minerals are similar to
sulfide minerals because both
contain the element sulfur.
Sulfate minerals and sulfide minerals are different because sulfide minerals contain one or
more elements combined with
sulfur, whereas sulfate minerals
contain one or more elements
combined with sulfur and
oxygen.
Section 1 • What Is a Mineral?
69