Key Terms:
rock, petrology, color, texture, grain,
coarse grain, fine grain, rounded, angular, spherical,
igneous rock, sedimentary rock, metamorphic rock
Rocks
 Please turn to page 45 in your textbook.
 Rocks are not minerals because they do not have all of
the characteristics of a mineral.
 Rocks are mixtures made of


Minerals
Other materials (pieces of other rocks or organic material).
 Geologists collect and study samples of rock in order
to classify and group them.
Stop :
Complete Classifying Rocks Power Point Notes Page 1 Part A
(Before Continuing)
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Petrology
Petrology is
the study of
the:
Petrology is
done
through the:
• Origin (how did the rock form) of the rock.
• Genesis (after forming how did the rock change
through time) of the rock.
•
•
•
•
•
Description of the rock.
Analysis of the rock.
Classification of the rock.
Where they occur.
Theories of their origin.
Stop :
Complete Classifying Rocks Power Point notes
page 1 Part B
Before Continuing
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Studying The Characteristics of Rock
 When studying a rock sample, geologists observe the 3
characteristics of the rock.
Color
 Texture
 Mineral Composition

 Using these characteristics, geologists can classify a
rock according to:


The rock’s origin (where it formed)
And how the rock formed.
Stop :
Complete Classifying Rocks Power Point Notes
page 1 Part C
Before Continuing
4
Stop
Pick up a copy of the
“Classifying Rocks Power
Point Worksheet 1” before
continuing.
5
1. Color
The overall color observed when
the rock is observed visually.

e.g. red-brown, grey-black, brown, grey,
yellow-brown, grey-blue, etc.
Not only is the color of the rock
observed, but also the shade of the
color.
 Dark
shaded
 Light shaded
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Rock Color Activity
 You will use Classifying
Rocks Power Point
Worksheet 1 part A for this activity.
 On the following slide, link to the picture of each
rock sample.
 After linking to the photo, use the color chart on
the previous slide. Try your best to determine the
color and the number for each of the rocks observed.
 Complete the chart on part A of your worksheet.
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Rock Color Activity
Rock Samples (click on the sample to link to the picture).
Rock Sample 1
Rock Sample 2
Rock Sample 3
Rock Sample 4
Rock Sample 5
Stop :
Complete Classifying Rocks Power Point
Worksheet 1 Part A
Before Continuing
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Stop
Pick up a copy of the
“Classifying Rocks Power
Point Notes Page 2” before
continuing.
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2. Texture
 Open your textbook to page 46.
 The look and feel of the rock’s surface.
 Very useful in identifying the rock.
 The texture of the rock is determined by the
grains that make up the rock.
 A grain is a particle of mineral or other
rock.
 Geologists use a number of terms based on
the rock’s grains to describe the texture of
Stop :
the rock.
Complete Classifying Rocks Power Point Notes
Page 2 Part A
Before Continuing
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Descriptive Grain Terms
 Grain Size

What size are the grains?
 Grain Shape

Do the grains have a distinct shape?
 Grain Pattern

Are the grains aligned in some kind of pattern?
 No visible grain

Can any grains be seen?
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Complete Classifying Rocks Power Point Notes
Page 2 Part B
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Grain Size
 Coarse grained
Grains are large and easy to see.
 Fine grained
 Grains are small and can only be seen
using a magnifying glass or microscope.
 No Visable Grain
 Grains cannot be seen even with a
Stop :
microscope of hand lens.

Complete Classifying Rocks Power Point Notes
Page 2 Part C
Before Continuing
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Grain Size Wheel Chart
Ex: #3 through 7: Coarse Grain
Ex: #8 through 10: Fine Grain
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Rock Grain Size Activity
 You will use Classifying
Rocks Power Point
Worksheet 1 part B for this activity.
 On the following slide, link to the picture of each
rock sample.
 After linking to the photo, use the grain size wheel
chart on the previous slide. Try your best to
determine the grain size (coarse, fine, or no visible
grain) and the wheel number (if applicable) for
each of the rocks observed.
 Complete the chart on part B of your worksheet.
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Rock Grain Size Activity
Rock Samples (click on the sample to link to the picture).
Rock Sample 1
Rock Sample 2
Rock Sample 3
Rock Sample 4
Rock Sample 5
Stop :
Complete Classifying Rocks Power Point
Worksheet 1 Part B
Before Continuing
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Grain Shape
 Grains vary in shape.
 Shape of the mineral crystals that make
up the rock.
 Shape of the fragments of other rocks.


Rounded grain
Jagged (angular) grain
Stop :
Complete Classifying Rocks Power Point Notes
Page 2 Part D
Before Continuing
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Rock Grain Shape Activity
 You will use Classifying
Rocks Power Point
Worksheet 1 part C for this activity.
 On the following slide, link to the picture of each
rock sample.
 After linking to the photo, use the grain shape
chart on the previous slide. Try your best to
determine the grain shape and how spherical the
grain is for each of the rocks observed.
 Complete the chart on part C of your worksheet.
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Rock Grain Shape Activity
Rock Samples (click on the sample to link to the picture).
Rock Sample 1
Rock Sample 2
Rock Sample 3
Rock Sample 4
Rock Sample 5
Stop :
Complete Classifying Rocks Power Point
Worksheet 1 Part C
Before Continuing
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Grain Pattern
 The grains in a rock often form patterns.



Flat layers (like stacks of pancakes)
Wavy swirling patterns
Banded rows of different colors
 In petrology, a rock whose grains form a layering or
banded pattern are known as foliated.
 In contrast, some have no pattern at all and the
grains occur randomly throughout the rock.
 In petrology, a rock whose grains form no pattern
are nonbanded and are known as non foliated.
Stop :
Complete Classifying Rocks Power Point Notes
Page 2 Part E
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Before Continuing
Rock Grain Pattern Activity
 You will use Classifying
Rocks Power Point
Worksheet 1 part D for this activity.
 On the following slide, link to the picture of each
rock sample.
 After linking to the photo, look to see if the grains
form a pattern.
 Complete the chart on part D of your worksheet.
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Rock Grain Pattern Activity
Rock Samples (click on the sample to link to the picture).
Rock Sample 1
Rock Sample 2
Rock Sample 3
Rock Sample 4
Rock Sample 5
Stop :
Complete Classifying Rocks Power Point
Worksheet 1 Part D
Before Continuing
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No Visible Grains
 Cannot see any grains even with the
use of a magnifying glass or
microscope.
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3. Mineral Composition
 Geologists identify the minerals that
make the rock.
Often done with using a small slice of
the rock and viewing the slice under a
microscope.
 Geologists also use some of the tests that
are used to identify minerals.

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