Download 7.1 Minerals: Building Blocks of Rocks

7.1
Minerals: Building Blocks of Rocks
Page 179
PRESCRIBED LEARNING OUTCOMES
Time
• compare the characteristics of the Earth’s core, mantle, and crust, and
describe the formation of rocks
30–45 min
KNOWLEDGE
• rocks are made of minerals that have unique properties
• minerals are made from pure elements in Earth
• minerals can be identified by their colour, lustre, hardness, cleavage,
crystal structure, and their reaction to certain chemicals
ICT OUTCOMES
• apply predetermined search criteria to locate and retrieve information
using information technology tools
SCIENCE BACKGROUND
• Diamond and graphite have the
same chemical formula (C), but their
properties are very different. What
we normally refer to as pencil “lead”
is really graphite. It is dark grey or
black and is very soft (1 to 2 on the
Mohs hardness scale). Diamond, on
the other hand, can be a variety of
colours and is very hard (10 on the
hardness scale). Diamond is formed
when carbon is subjected to very
high temperatures and pressure.
Colour
• Colour is a property of minerals that
is easy to see but can be misleading,
as the same mineral can occur in
several different colours.
• Quartz is the most common mineral
on Earth and comes in many colours.
Clear (colourless) quartz is the most
common, followed by white or milky
white. But purple quartz (amethyst),
pink (rose quartz), grey or brown to
black (smoky quartz) are also
common.
• Similarly, hematite is a common
mineral that is found in several
colours—silver-grey, grey, black
(“Alaska black diamond”), red (red
ochre pigment), reddish-brown, and
brown.
Streak
• Streak describes the colour or
powdery mark that a mineral makes
on a streak plate, an unpolished
porcelain tile. Streak is more reliable
NEL
Key Ideas
Minerals are the building
blocks of rocks and can be
identified by their physical
properties:
• colour
• streak
• lustre
• hardness
• crystal structure
• cleavage
• magnetism
• reaction with certain
chemicals
Vocabulary
than colour in identifying minerals
because the colour of the streak
remains constant for a mineral even
when the colour of the mineral varies.
• Clear, milky, white, pink, purple, grey,
brown, and black quartz all leave a
white streak. All colours of hematite
produce a blood-red streak (the root
of the name hematite comes from
the Greek word meaning blood, the
same root as the word hemoglobin).
In this way, the streak test can help
confirm that different-coloured
samples of a mineral are the same
mineral. It can also help distinguish
between minerals that are similar.
For example, galena and hematite
both have metallic lustres and are
denser than average, but hematite
has a red-brown streak and galena
has a dark grey or black streak.
• minerals
Skills and Processes
Observing
Lesson Materials
per student
• rock samples (2 or 3)
• magnifying lens (optional)
Program Resources
BLM 0.0-7 Four-Column Table
SM 7.1 Minerals: Building
Blocks of Rocks
Nelson Science Probe 7
Web site
www.science.nelson.com
Lustre
• Lustre is the degree of shininess or
the way the surface of a mineral
reflects light. It is best to observe
lustre where a mineral has been cut
or on an untarnished surface. The
two general types of lustre are
metallic and non-metallic. There is no
fixed list of descriptors, but rather a
variety of terms are used to describe
lustre, including the following:
– adamantine, or brilliant (like a
diamond)
– vitreous, resembling glass (like
obsidian)
– metallic (like galena)
Chapter 7
Old rocks can be recycled into new rocks.
357
Related Resources
Hankin, Rose (ed). Rocks,
Crystals, and Minerals.
Burnaby, BC: Select
Publications, 2004.
Staedter, Tracy. Rocks and
Minerals. New York, NY:
Reader’s Digest
Children’s Pub., 2004.
Stewart, Melissa. Minerals.
Chicago, IL: Heinemann
Library, 2002.
Stewart, Melissa. Crystals.
Chicago, IL: Heinemann
Library, 2002.
Vancouver Rocks (poster)
Vancouver, BC:Geological
Survey of Canada, 2004.
Sales and Publications,
101–605 Robson St.,
Vancouver, BC V6B 5J3,
604-666-0271
Geologist’s Notebook:
What Exactly Are
Minerals? (video).
Vancouver, BC: B.C.
Learning Connections,
Inc., 2003. (604) 3247752; 1-800-884-2366
– greasy or waxy (like turquoise)
– pearly (like talc)
– silky (like some fibrous minerals
such as asbestos)
– dull, or having a matte finish
Hardness
• The Mohs hardness scale is easy to
use. For example, if a mineral
sample cannot be scratched by
feldspar (6), but it can be scratched
by quartz (7), then its hardness is
between 6 and 7. Pyrite is a mineral
that has a hardness of 6 to 6.5.
Using common objects is easy as
well. For example, if a mineral
sample cannot be scratched by your
fingernail (2 to 3), but can be
Unit C: Earth’s Crust
Crystal Structure
• Minerals usually crystallize into one
of six crystal shapes. The axes of the
crystal, the angles at which the axes
intersect, and the degree(s) of
symmetry are used to categorize
crystals in one of the six shapes.
• The shape of a crystal is the main
identifier. There are six main crystal
systems with 32 possible classes of
crystals within these systems. The
six main crystal systems are
described in the following table:
Class of crystal
Description
Example(s) of mineral
isometric
three axes, all perpendicular
to one another and equal in
length
pyrite, galena, halite (salt),
gold, diamond
tetragonal
three axes, all perpendicular
to one another, with two of
equal length
zircon
orthorhombic
three axes, all perpendicular
to one another, and all of
different lengths
topaz, olivine
monoclinic
three axes of unequal length;
two of the axes are oblique
(i.e., not perpendicular) to
one another but both are
perpendicular to the third
axis
gypsum, orthoclase, talc
triclinic
three axes of unequal length
and oblique to one another
plagioclase feldspar,
microcline
hexagonal
four axes, three of which are
in a single plane, evenly
spaced, and of equal length;
the fourth axis is
perpendicular to the other
three
quartz, graphite, beryl,
molybdenite, pyrrhotite
Cleavage
• Cleavages are breaks that happen
along planes of weakness in the
crystal structure of a mineral. Some
minerals break only in one direction,
while others break in two or more. If
a mineral breaks easily and cleanly in
one or more directions, its cleavage
is considered perfect. Calcite cleaves
perfectly along three planes. Some
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scratched by a penny (3 to 4), then
its hardness is in between the two.
Calcite is a mineral that has a
hardness of 3.
minerals cleave perfectly in one
direction but poorly in others. For
example, gypsum cleaves perfectly
along one plane but poorly along two
others.
• Cleavages are usually clean, flat
breaks. Minerals that don’t cleave
are said to fracture; that is, the
breaks are irregular, curved, jagged,
or splintery.
NEL
Magnetism
• Magnetism can be used to identify a
mineral sample that contains the
element iron. If a mineral sample is
attracted to a magnet, then we say
that it is magnetic and we know that
it contains iron.
• Magnetite (iron oxide) is a natural
magnet. It contains a lot of iron (both
Fe2+ and Fe3+), and therefore will
attract another magnet or any object
containing iron.
Reaction with Certain Chemicals
• If a mineral cannot be identified by
its physical characteristics, then
chemical analysis may be done.
Solubility in acids is one way to
identify minerals. Some minerals,
like gold, are only very slightly
soluble. Some are soluble in one
acid but not in another. For example,
copper dissolves in nitric acid only.
• Calcite, limestone, marble, and any
rock or mineral that contains the
carbonate group (CO3) will fizz and
give off carbon dioxide in reaction
with acidic solutions.
• Other chemical indicators include the
gases a mineral produces (for
example, because of its sulfur
content, the mineral sphalerite
produces a rotten egg smell when
dissolved in hydrochloric acid) and
what happens when a mineral is
placed in a flame (for example,
different minerals produce different
flame colours).
TEACHING NOTES
• The Try This activity encourages students to find rocks that are
different from each other. For comparison purposes, ensure that you
have on hand several samples of rocks that are common to the local
area.
1 Getting Started
• Check for Misconceptions
– Identify: Students may think that colour is more valuable
as an identifying property than it actually is.
– Clarify: Use rock samples or photos of a variety of colours of
quartz or hematite. If you have samples, show that the streak is the
same colour for a variety of colours of quartz (white) or hematite
(blood-red).
– Ask What They Think Now: Ask students which one test they could
do to identify quartz or hematite.
• Have students brainstorm what they know about rocks and minerals.
Record their ideas on chart paper and post. This information may be
useful for identifying misconceptions, which can be dealt with
during the lesson.
• Have students complete the Try This: Observe Rocks. Students can
use BLM 0.0-7 Four-Column Table to record their observations.
NEL
Chapter 7
Old rocks can be recycled into new rocks.
359
TRY THIS: OBSERVE ROCKS
Purpose
• Students will carefully observe rocks to determine their differences.
Notes
• Reinforce the importance of looking for differences in as many different
categories as possible, for example, sharpness, colour, feel/ texture, composition,
density.
• Provide students with magnifying lenses so they can observe their samples
closely.
Suggested Answers
• Students’ answers will vary depending on their rock samples. Students should
record as many different characteristics as possible. Ensure that students record
observations, not inferences; for example, students should record colour, streak,
etc., and not make inferences about what they think the rock is made from.
2 Guide the Learning
• Have students scan the section to find the eight properties of
minerals. List them on the board. Ask students if they used any of
these when they were observing rocks in the Try This activity.
• Draw students’ attention to the Learning Tip on page 180. Use
Reading and Thinking Strategies: Anticipate Structure to prepare
and guide students in their reading and note-taking.
• Ask students which properties they think would be the most
important in identifying a mineral, and why.
• For students who need additional support with the reading in this
section, use SM 7.1 Minerals: Building Blocks of Rocks.
3 Consolidate and Extend
• Assign the Check Your Understanding questions.
CHECK YOUR UNDERSTANDING—SUGGESTED ANSWERS
1. The eight properties that are used to classify minerals are lustre, hardness,
colour, streak, magnetism, cleavage, crystal structure, and chemical reaction
with certain chemicals.
2. One advantage of using colour to identify a mineral is that colour is easy to see.
One disadvantage is that different minerals may be the same colour, for
example, fool’s gold and gold are both yellow.
3. Geologists use both colour of a mineral and the colour of its streak to identify
the mineral because some minerals occur in different colours, but their streaks
will always be the same.
4. Geologists use drill bits covered with small diamonds to drill into Earth’s crust
because diamond is the hardest mineral in the Mohs hardness scale, so it is
harder than most other minerals. Drill bits made from diamonds will cut through
most minerals in Earth’s crust.
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Unit C: Earth’s Crust
NEL
Reading and Thinking Strategies: Anticipate
Structure
• Direct students’ attention to the structure of the text
under the heading Colour.
• Read the paragraph to them, pointing out the three
parts in the pattern:
– explains what the test is or does (easy to determine,
important clue, but not always reliable)
– gives examples (gold and pyrite are both yellow)
– illustrates the ideas in photos and captions (jade is
usually green, quartz is sometimes colourless)
• Have students read the text and view the photos under
the heading Streak, to see if they can find the same
pattern.
• Ask students to read to the end of the section to see
which paragraphs follow the pattern.
• Discuss how they can use patterns in structure to help
them make notes to summarize the content of each
subsection.
LEARNING TIP
Colour
Preview the next four
pages. Each heading is a
property. Under each
heading, the property is
explained and you are given
examples in both words and
photographs. Make notes
using this structure.
Colour is easy to determine and can be an important clue to a
mineral’s identity (Figure 2). By itself, however, colour is not a reliable
way to identify minerals. Different minerals may be the same colour.
For example, both gold and pyrite (fool’s gold) are yellow. Some
minerals occur in many different colours. For example, quartz is often
white, but it can also be violet, gray, black, or colourless (Figure 3).
Figure 2
Figure 3
Jade is usually a shade of green
Quartz is sometimes colourless.
Streak
Streak describes the colour of the powdery mark that some
minerals make when they are scratched against a hard surface. To
see the streak clearly, geologists scratch a mineral on a streak plate.
A streak plate is an unpolished piece of porcelain tile. The colour
of the streak may be the same as the colour of the mineral, or it
may be different. The colour of the streak is more reliable than the
colour of the mineral. For this reason, it is very useful for
identifying some minerals. For example, hematite can be shiny
silver or reddish, but it always has a reddish streak (Figure 4).
Pyrite (fool’s gold) and gold are both yellow, but gold makes a
yellow streak and pyrite makes a dark streak (Figure 5).
Art Connections
180
Unit C
Figure 4
Figure 5
Different colours of hematite make the
same colour streak.
During the gold rush, prospectors used
streak to test if they had found real gold.
Earth’s Crust
NEL
Graphite pencils are used in drawing or sketching. Artists’
pencils come in different hardnesses, graded from B (for
blackness) to H (for hardness), and F (for fine point) as
follows: 9H 8H 7H 6H 5H 4H 3H 2H H F HB B 2B 3B 4B
5B 6B 7B 8B 9B, with 9B being very soft and 9H being
very hard. The American system of rating the hardness of
pencils uses a number only, as follows: #1 = B, #2 = HB
1
(most common), #22 = F, #3 = H, and #4 = 2H.
Meeting Individual Needs
Extra Challenge
• Have students research a mineral of their choice. Have them collect
facts on colour, streak, lustre, hardness, crystal structure, cleavage,
magnetism, and reaction with certain chemicals. This information can
be added to a class chart, similar to “Characteristics of Some Common
Minerals” on page 186 of the student book.
www.science.nelson.com
GO
Extra Support
• For students who need additional support with the reading in this
section, use SM 7.1 Minerals: Building Blocks of Rocks.
ASSESSMENT FOR LEARNING
What To Look For in Student Work
Suggestions for Teaching Students Who Are Having Difficulty
Evidence that students can
• observe and identify minerals using their
physical properties (e.g., colour, streak,
lustre, hardness, crystal structure,
magnetism, reaction to acids, cleavage)
• use technical language correctly (e.g.,
minerals, names of physical properties)
If students have difficulty identifying properties and tests because they are not
fluent in English or have trouble learning the scientific terminology, use the photos
and art in the student book and hands-on materials to review properties and tests.
The ability to identify properties and match tests to properties is more important
here than precise terminology.
NEL
Chapter 7
Old rocks can be recycled into new rocks.
361