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Geology 1 – Physical Geology

Lessons, Activities, and Labs David Bazard and Emily Wright

College of the Redwoods

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Contents Lesson One: Introduction ................................................................................................ 1

Worksheet 1.1 ............................................................................................................. 1

Lesson Two: Plate Tectonics ........................................................................................... 3

Worksheet 2.1: Earth Layers ........................................................................................ 3

Worksheet 2.2 Plate Boundaries .................................................................................. 4

Worksheet 2.3: Plate Boundary Table .......................................................................... 7

Lab 2.4: Using GPS to Study Plate Tectonics .............................................................. 8

Lab 2.5: Using magnetic properties of rocks to investigate plate motions ................... 15

Lesson Three: Minerals ................................................................................................. 21

Background Reading Part I: Basic Chemistry of Rock Forming Minerals .................. 21

Worksheet 3.1: Basic Chemistry of Minerals ............................................................. 24

Background Reading Part II: Mineral Identification ................................................... 25

Lab 3.2: Known Minerals ......................................................................................... 27

Lab 3.3: Unknowns ................................................................................................... 28

Lab 3.4: Special Minerals .......................................................................................... 29

Lesson Four: Igneous Rocks .......................................................................................... 31

Background Reading: Igneous Rocks ........................................................................ 31

Worksheet 4.1: Igneous Rocks ................................................................................... 35

Lab 4.2: Igneous Knowns .......................................................................................... 38

Lab 4.3: Igneous Rock Unknowns ............................................................................. 39

Igneous Rock Lab Quiz – Review Sheet .................................................................... 41

Lesson Five: Volcanoes ................................................................................................. 43

Background Reading: Volcanoes ............................................................................... 43

Worksheet 5.1: Volcanoes ......................................................................................... 46

Lesson Six: Weathering and Sedimentary Rocks ........................................................... 49

Background Reading: Sedimentary Processes ............................................................ 49

Worksheet 6.1: Sediment ........................................................................................... 54

Lab 6.2: Analyzing Sediment..................................................................................... 57

Lab 6.3: Sedimentary Knowns ................................................................................... 58

Lab 6.4: Sedimentary Unknowns: .............................................................................. 59

Lesson Seven: Metamorphic Rocks ............................................................................... 61

Background Reading: Metamorphic Rocks ................................................................ 61

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Worksheet 7.1: Metamorphic Rocks .......................................................................... 66

Lab 7.2: Metamorphic Minerals and Known Metamorphic Rocks .............................. 69

Lab 7.3: Unknown Metamorphic Rocks: .................................................................... 70

Sedimentary and Metamorphic Rock Lab Quiz - Study Guide ................................. 72

Lesson Eight: Structural Geology .................................................................................. 75

Background Reading: Structural Geology .................................................................. 75

Worksheet 8.1: Moonstone Beach Field Trip Preparation .......................................... 79

Worksheet 8.2: Geologic Structures ........................................................................... 83

Lab 8.3: Geologic Maps ............................................................................................ 85

Lesson Nine: Geologic Time ......................................................................................... 91

Background Reading: Geologic Time ........................................................................ 91

Worksheet 9.1: Relative Time.................................................................................... 94

Worksheet 9.2 -Absolute Time .................................................................................. 95

Worksheet 9.3: Geologic Time Scale ......................................................................... 97

Lab 9.4: Geologic Map of California ......................................................................... 98

Lesson Ten: Landscape Evolution ................................................................................. 99

Background Reading: Topographic Maps .................................................................. 99

Background Reading: Landforms ............................................................................ 100

Worksheet 10.1 - Mass Movement........................................................................... 103

Worksheet 10.2 - Rivers .......................................................................................... 104

Worksheet 10.3 Landscapes ..................................................................................... 105

Lab 10.4: Topographic Maps. .................................................................................. 106

Lab 10.5 Maps of Landscapes .................................................................................. 107

Name:_______________________________________________________ Date:______

GEOL1 Physical Geology Laboratory Manual College of the Redwoods

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Lesson One: Introduction

Worksheet 1.1

Read the discussion below. This discussion is similar to any paragraph that you might

select at random from an introductory geology textbook. When you are reading about

science, you might find yourself focusing on facts that have been discovered. It is

important to learn these facts to understand what scientists know about how the world

works, but to really appreciate science you must also appreciate that science is the process

by which people discover these facts. The questions below will help guide you thinking

about the science that you read in terms of the scientific process.

Discussion: (1)Geologists tell us that the explosiveness of a volcanic eruption is related to

the amount of a material called silica that is in the magma (liquid rock) of a volcano. Silica

is made of the elements silicon and oxygen and is the same material found in a mineral

called quartz. (2)This conclusion is based on looking at the most explosive volcanic

eruptions and finding that they produce quartz rich volcanic rocks. (3)Also, scientists have

found, through lab and field studies, that magma with a higher silica content is “thicker “

(more viscous) than magma with a lower silica content. This is similar to how honey is

“thicker” than water. (4)Geologists have used this information to come up with the idea

that higher silica content makes lava thicker, and thicker magma can hold gas under higher

pressure. (5)When high pressure gas comes to the surface it erupts more explosively than

gas trapped in a “thinner” (less viscous) liquid. The same process occurs when oatmeal

boils. When the bubbles in oatmeal “pop”, they explode and create a bigger mess than a

pan of boiling water.

1. Assign each numbered sentence to one of the following categories

Observations/Data: Things that have been directly observed or measured

by the researchers. They must be repeatable, meaning the observation

can be made either multiple times or was observed by multiple groups of

people.

Interpretations: The simplest explanation that fits all of the data and

observations. An interpretation is always subject to change based on new

observations.

2. State the overall hypothesis of the discussion above.

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3. Write a brief description of a lab experiment that would test this hypothesis.

4. Write a brief description of a field study that would test this hypothesis.

5. Choose one of your studies above and make a testable prediction about the

outcome of the study.

Example of a Testable Prediction:

Hypothesis: The hill between the College of the Redwoods parking lot and the

central part of the main campus was formed by the movement of a fault.

Prediction: A trench dug across the uphill edge of the College of the Redwoods

main parking lot would reveal soil and sediment layers that have been offset

vertically.

Name:_______________________________________________________ Date:______


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Lesson Two: Plate Tectonics

Worksheet 2.1: Earth Layers

1. On the left part of the diagram below, label the following layers: inner core, outer

core, lower mantle, upper mantle, oceanic crust, continental crust.

2. On the right part (the blow up) of the diagram draw a line representing the base of

the lithosphere, then shade in and label the area that is part of the lithosphere.

3. On the bottom of the left diagram, add an arrow pointing to the Mohrovicic

Discontinuity and label it “Moho”.

Figure: Emily Wright, 2017

4. Assume the lithosphere is 100km thick. Assume the earth has a radius of

6370 km. Determine the radius of the classroom globe and use a comparison

(ratio) to determine how thick the lithosphere would be on this globe to

represent a scale model of the actual earth (show your work).

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Worksheet 2.2 Plate Boundaries

1. The flow chart below will help you organize your thinking about Plate Tectonics

and Plate Boundaries. This may be slightly different than the way that the

concepts were organized in your textbook. Complete the chart by filling in the

missing words.

2. Sketch a Cross Section View of the Mid Atlantic Ridge. Include the continents

South America and Africa in your sketch. Your sketch will not be accurately

scaled, but make sure that you include: a. The Mid Ocean Ridge (MOR)

b. Arrows in the tectonic plates showing the direction of plate motion

c. Oceanic Crust

d. Continental Crust e. Lithosphere

f. Arrows in the Mantle showing convection

g. Area of Partial Melt (where the magma is made)

Plate Tectonics

Plate Boundaries

Convergent

Ocean to Ocean Convergence

Mid Ocean Ridge

Name:_______________________________________________________ Date:______


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3. Sketch a Cross Section View of the Cascadia Subduction Zone. Your drawing

should include: a. Arrows in the tectonic plates showing the direction of plate motion

b. Oceanic Lithosphere* c. Continental Lithosphere*

d. Mantle (the non-lithospheric mantle)

e. Area of partial melt (where the magma is made)

f. Trench g. Volcanic Arc Mountain Range

*You can leave out the crust and the Moho to make this drawing a little cleaner.

4. Sketch a Map View of the Hawaiian Hot Spot Island Chain. Your drawing should

include: a. An arrow showing the direction of plate motion b. An active volcanic island

c. Older volcanic islands

d. Seamounts

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5. Consider the three plates (ABC) shown in the figure below (Figure: David Bazard, 2012). The

boundaries are shown by standard map symbols. The arrows show relative plate motion. These may vary on the same plate because they show the relative motion between two

plates at a single location, not the absolute plate motion. Note: This is a hypothetical

situation, not California (although some parts are very similar).

For each numbered location (1-5) provide:

The type of stress expected

The name of this type of plate boundary

A

B

Location #1

Stress:

Plate Boundary:

Location #2

Stress:

Plate Boundary:

Location #3

Stress:

Plate Boundary:

Location #4

Stress:

Plate Boundary:

Location #5

Stress:

Plate Boundary:

C

Name:_______________________________________________________ Date:______


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Worksheet 2.3: Plate Boundary Table

Complete the following table.

Boundary Type Sense of relative motion Map Symbol Principal Stress Important Features Earthquakes Volcanoes

Transform

Transform

Shear

Faults

Offset markers

Yes

No

Subduction

Zone

Continental

Collision

Mid Ocean

Ridge

Continental

Rift

Hot Spot

N/A

N/A

N/A

C

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Lab 2.4: Using GPS to Study Plate Tectonics

(public domain text and figures from UNAVCO) UNAVCO is a non-profit membership-governed university consortium that facilitates geoscience research and education using geodesy. In the US, UNAVCO operates the Plate Boundary Observatory (PBO) as the geodetic component of the US EarthScope program.

The global positioning system (GPS) is a fleet of 29 satellites that are orbiting our planet

approximately 11,000 miles above Earth’s surface. A position can be calculated using at least

three satellites. High precision GPS can calculate a position to the nearest millimeter (hand-

held units only get down to about 1 meter).

When deformation occurs a point on Earth’s surface changes. The position change can be

measured using high-precision GPS instruments. Earth scientists use these data to record how

much and how quickly Earth’s crust is changing because of plate tectonics and to better

understand the underlying processes of the deformation. Each station continuously records its

position. A plot of the station's changes in position is called a time series. Each station has time

series for north-south, east-west and up-down motions. Southward or westward motions are

shown as either negative north (for south) or

negative east (for west).

The photograph shows a high precision GPS

station (P162) located on Table Bluff, near the

CR campus. The time series plot on the next

page shows the position change recorded in

millimeters (mm). The changes are relative to a

Stable North America Reference Frame -SNARF

(the interior portion of the North American

plate). For a color photo and unpdated data

search “UNAVCO P162”.

The following figure shows how to interpret the time series plots. Complete the bottom right

portion of the figure.

http://en.wikipedia.org/wiki/EarthScope

Name:_______________________________________________________ Date:______


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Questions: 1. In what general direction has this site been moving in the last twelve years?

2. Is it moving up or down?

3. By January 2017, how far north had P162 moved since it’s installation in 2005?

4. An average how much does P162 move northward per year? Your answer should have

the units mm/yr (millimeters per year).

5. Multiple choice: The units mm/yr express a measure of ________. a. Distance

b. Time c. Velocity (speed)

d. Volume

6. Calculate the eastward velocity of P162 using the same method that you used for the

northward velocity.

Name:_______________________________________________________ Date:______


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7. A vector is an arrow that shows both direction and a magnitude. In this case the

magnitude is the velocity. Use the plot below to plot the appropriate vector. There is

an example on page 13 help guide you.

You might be interested in knowing the total horizontal velocity of the GPS station and the

precise direction that it is moving. You can determine these things either graphically or

algebraically. The algebraic solutions will be more accurate (if done properly) but require

some math background. You may choose the method that is most appropriate for you.

8. Determine the total horizontal velocity of P162. Choose one of the two methods and

indicate the method you used.

a. Graphical method: measure the length of the vector (diagonal line) that you

have drawn on your plot using the scale of the graph paper.

b. Algebraic method: Use the Pythagorean Theorem to calculate the length of the

vector (the hypotenuse). Hint: It is important to remember order of operations

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9. Determine the precise direction in azimuth. (Azimuth is a method of reading a compass

as a 360-degree circle where North is 0°, East is 90°, South is 180° and West is 270°.

a. Graphical method: extend your vector onto the circle in the diagram and read

the number on the circle. (See page 13 for example).

b. The algebraic method is more advanced this time. You will need some

trigonometric relationships (think: “soh cah toa” …if that means nothing to you,

stick to the graphical method)

10. Draw the appropriate vector for P162 on the map below. To get the right length arrow,

estimate based on the 25 mm/yr reference arrow in the lower left corner. Work in

pencil first, then when you are confident, ink in your final arrow.

Name:_______________________________________________________ Date:______


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Example Vector Plot: Station C Moves: 3 mm/yr North and 6 mm/yr East

Step 1: Polt the North and East

Vectors

Recall that negative velocities will

be South or West

Step 2: Plot the Final Vector

Trace a horizontal line from the head of the North and a verical line from the head of the East

vector, then draw a new vector with the tail at the center of the plot and the head at the

intersection point of your two lines. This is your final vector.

Step 3: Find the azimuth direction for the vector

Extend the arrow to the circle and read the azimuth direction.

Station C is moving 66° with a velocity of 6.7 mm/yr

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11. The map below shows the motions of several southern California GPS stations.

Describe how Barstow is moving relative to Los Angles. In other words, if you were in

Los Angles, Barstow would appear to be moving ________________.

12. Using the information from the previous question, add half-arrows along the San

Andreas Fault (SAF) in the map above, that show the relative sense of motion. (See the

example on the right)

The map at right shows average GPS position

movements relative to the stable interior of the

North American plate. Each vector shows the

direction of motion of a point on the crust. Vector

length indicates speed in mm/year.

13. Use the information you learned above to

approximate the location of the SAF. Draw

in the plate boundary on the map.

14. What other interesting patterns do you notice

in the GPS veolicities?

Examples of Half Arrows:

USGS Public Domain

Name:_______________________________________________________ Date:______


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Lab 2.5: Using magnetic properties of rocks to investigate plate motions

When rocks form they can acquire and record the current state of the Earth’s magnetic

field at the location of their formation. Minerals of igneous rocks align with the

prevailing magnetic field to produce a record of the magnetic field orientation at the time

of crystallization. We think of the current magnetic field orientation as Normal. This

means there is a magnetic attraction toward the north magnetic pole (near the north

geographic pole) and a magnetic repulsion away from the south magnetic pole. An iron-

rich igneous rock forming today would record a normal orientation.

(USGS Public Domain)

At various times in the past the orientation has been reversed. A rock crystallizing at this

time would have a magnetism pointed toward the south magnetic pole. The magnetic

time scale below provides a record of when the Earth’s magnetic field was either normal

(black bars) or reversed (white bars). Each time period is given an anomaly number. The

age is shown in millions of years (Ma).

(USGS, Public Domain)

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The map on page 19 shows magnetic anomalies that have been mapped in the Atlantic

Ocean. The numbered lines repesent the numbered anomalies in the timescale on page

15. For example, the line with the number 8 represents oceanic crust that was formed

during anomaly 8, about 27 million year ago. Confirm that you can find this age using

the chart. There is an anomogy 8 line on either side of the Mid Atlantic Ridge, but the

lines are not straight. They have been offset by transfrom fault zones such as the Bode

Verde Fault Zone. Find two places where the Bode Verde F.Z. offsets anomaly 8.

In the following exercise you will use the pattern of magnetic lineations (anomalies) to

restore the positions of Africa and South America at the time the magnetic anomaly was

being formed on the Mid-Atlantic Ridge.

1. We will use anomaly number 21 for this exercise. Use the magnetic reversal time

scale on page 15 to determine the age of magnetic anomaly 21.

2. Use the figure on page 19 and these instructions to complete this section.

First: draw a colored line over each of the magnetic lineations of anomaly

number 21 on the South American side of the Mid-Atlantic Ridge (do not

color the African side). Connect the anomaly lines by also drawing over the

transform boundaries that separate the anomaly 21 lineations.

Second: Place a piece of tracing paper over the figure and hold it in place with

tape or paper clips. Repeat the process described above for anomaly 21 on the

African side of the Mid-Atlantic Ridge. Note that anomaly 21 should be

colored on the figure only for the South American side and it should be

colored on the tracing paper only for the African side.

Third: With the tracing paper in place, trace the coastlines of Africa and

South America on the tracing paper with black pencil. Also use a black pencil

to trace the boundaries of the figure (the box) and the 20 degree South latitude

line.

Fourth: Detach the tracing paper and slide it toward the South American side

until the colored line on the tracing paper matches the colored line on the

figure. When the two lines are matched as closely as possible, hold the

tracing paper in place and trace the coastline of South America in colored

pencil on the tracing paper. Also trace the 20 degree South line on the tracing

paper in color.

3. The map you have constructed on the tracing paper shows the Mid-Atlantic Ridge

as it existed when magnetic anomaly 21 was being formed. Your tracing paper

also shows the relative positions of segments of the coastlines of Africa and South

America as they were at the time of anomaly 21.

Name:_______________________________________________________ Date:______


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4. What is the evidence that the movement of the plates from magnetic anomaly 21

time to present was not strictly in an east-west direction?

5. We will now determine the rate at which the Atlantic Ocean is growing. In other

words, the speed at which Africa is moving away from South America.

a. At the northern most end of the Mid Atlantic Ridge that is pictured, how

far has anomaly 21 moved from the ridge? (Use the bar scale on the map)

b. Have both sides moved the same amount? If not, how much has the other

side moved?

c. How much has the width of the ocean increased in this location since

anomaly 21 formed?

d. Now use this answer and your answer from question 1 to determine the

rate that the Atlantic Ocean is spreading. In this case the rate is a velocity.

You will recall that Speed = Distance/Time. Express your answer in the

units km/Ma (Ma = millions of years ago).

e. Convert your answer to mm/yr. Show your work.

6. Compare your answer to the previous question to the speeds (velocities) that you

worked with in Worksheet 2.1. Does your answer seem reasonable for the speed

of tectonic plates? If not, why might that be

7. Is the southern end of the Mid Atlantic Ridge spreading at the same rate as the

northern end or is it faster or slower? How can you tell?

Name:_______________________________________________________ Date:______


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Name:_______________________________________________________ Date:______


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Lesson Three: Minerals Background Reading Part I: Basic Chemistry of Rock Forming Minerals

Minerals are defined as having a definable chemical composition. For example,

the mineral quartz always has the composition of SiO2. This means it is made of building

blocks that include one silicon atom linked to two oxygen atoms. You can think of these

as Lego blocks that are all the same. A single crystal may have millions of these blocks

all stacked together to make the crystal that you hold in your hand. To understand

minerals, we must understand what we mean by an element (such as silicon or oxygen),

and how the presence of certain elements and their linking together (bonding) influences

the mineral properties such as hardness, color, density, ability to cleave, and crystalline

form.

In addition, it is important to recognize that although minerals have a definable

chemistry, they can appear different due to a slight impurity added to the mineral

chemistry. For example, amethyst (beautiful purple colored mineral) is really just quartz.

However, a small amount of iron has been added to the SiO2chemistry. It may help to

think of these impurities as being like a drop of food coloring added to an ice cube. The

ice is still basically H2O, but adding food coloring can result in green ice, even though the

coloring represents less than 1% of the composition of the ice cube. Likewise, Rose

Quartz takes its color from impurities of titanium within the crystal.

Here are some basic aspects of chemistry we need to understand minerals:

Element: a substance that cannot be decomposed into simpler substances by ordinary

processes. There are 92 naturally occurring elements. The atom is the smallest particle

that exists as an element.

Common Elements in the crust: Oxygen (O), Silicon (Si), Aluminum (Al), Iron (Fe),

Magnesium (Mg), Calcium (Ca), Potassium (K), Sodium (Na)

The table below lists the common elements found in the crust.

Negative Anion Positive Cation

O2-

Si4+

Al3+

Fe3+

Mg2+

Fe2+

Na1+

Ca2+

K1+

Note that the elements listed in the table above are listed as either negative or

positive ions (Anion or Cations).

What is an ion?

Ions: An atom or molecule that possesses an electrical charge. This is due to an atom

gaining or losing an electron.

Cations (positive charge, lost electrons), Anions (negative charge, gained electrons)

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In order to understand why ions form, we need to understand the basic structure of an

atom. Atoms are composed of a nucleus with neutrons and protons and a surrounding

electron cloud. The neutrons have no charge, the protons have a positive charge, and the

electrons have a negative charge. The positive and negative charges attract so the protons

attract the negative charge of the electron cloud.

(Public Domain image – Google public domain images)

The number of protons in the atom’s nucleus defines the element. So, for example,

Oxygen shows up on the periodic table as 8, because it has 8 protons in its nucleus.

Silicon (Si) has 14 protons and it is listed as number 14 on the periodic table.

Ideally, there is a balance between the number of protons and electrons to make the total

charge of the atom zero. Thus you might predict that Oxygen would have 8 protons and

8 electrons. This would be +8 and –8. Add these together and you get zero.

However, there is a “tendency” of some atoms to gain or lose electrons. Oxygen has a

tendency to gain two electrons. When this happens it then has +8 (protons) and –10

(electrons). This causes the total charge to be –2, (because +8 –10 = -2). This tendency

is represented on the table of common elements presented above as O2-

. When an atom

has a negative charge, like oxygen, we call it an Anion.

So, here’s the tricky part – what made oxygen an anion? Was it the gaining of electrons

or the loss of electrons? If you say gaining electrons, you are correct. This means that a

gain of electrons makes an ion negative. Do you see why this can be confusing? It is a

gain of something (negative electrons) that makes the atom negative, or an anion.

Following this same pattern, if an atom loses electrons (which are negative), the atom

becomes more positive. If the atom has a positive charge it is called a Cation.

A way to remember that cations are positive (and anions are negative) is to remember

that the word “cation” has the letter “t” and that the “t” looks like a plus sign. Also

the prefix “a” or “an” means “not” or negative. If something is “atypical” it is not

typical. Thus, an anion is negative.

Name:_______________________________________________________ Date:______


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Notice that most of the common elements in the earth’s crust are cations (Silicon, Iron,

Potassium, Calcium, Sodium, Aluminum, Magnesium). Oxygen is the only common

anion in the table above.

Why do we care about ions?

Since positive and negative charges attract, anion and cations will attract and form

compounds. These are building blocks of minerals. Look again at the table of common

elements in the earth’s crust. Notice that there is only one anion in this table. That

means that this particular anion (oxygen) has to be involved in a lot of the “gluing

together” of ions to form minerals. For this reason, Oxygen is the most common element

in the Earth’s crust. It seems strange, but when you are walking across a rocky field,

beach, or mountain top, you are walking mostly on oxygen!

We call the process of ions “gluing together” – Bonding.

Two common types of atomic bonds are ionic and covalent bonding.

A bond that forms due to the exchange of electrons between a positive cation and a

negative anion is called an Ionic Bond. The key word in this definition is exchange.

Ionic bonding is due to an exchange of electrons. Common table salt (sodium

chloride) is formed due to ionic bonding of Na+ and Cl

-

An ionic bond tends to be weaker than a covalent bond. Thus, salt is not very hard.

Bounding that involves the sharing of electrons is called Covalent Bond. In this case

one electron actually occupies the outer electron cloud of two atoms at once (yes, this is

strange) and provides the added negative charge to pull the two atoms together. The key

word in this definition is sharing. Covalent bonding is due to the sharing of electrons.

Diamonds are covalently bonded carbon atoms.

A covalent bond tends to be stronger than an ionic bond. Thus, diamond is very hard.

Why do we care about bonding?

Bonding determines mineral composition.

Bonding explains properties: hardness, cleavage, color, crystalline structure

Bonding explains tendency to change: oxidation, leaching of elements.

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Worksheet 3.1: Basic Chemistry of Minerals

Silicon (Si) has a tendency to lose 4 electrons. This results is a charge of _____ 1.

Oxygen (O) has a tendency to gain 2 electrons. This results is a charge of _____ 2.

Which one of the two ions described above is considered a cation? ________ 3.

Use your answers from 1 and 2 to determine the charge of SiO4. Assume the 4.

charges you listed as the answers as the charges for each atom in the molecule

SiO4. Remember SiO4 consists of one silicon atom and four oxygen atoms, so

you will need to add up the total charge for one silicon atom and four oxygen.

How many Magnesium ions does the SiO4 ion need to bond with to provide a 5.

neutral charge? The charge for Magnesium results from losing two electrons.

This is the formula for the mineral Olivine (gem quality olivine is called peridot)

A common way for minerals to form is through the cooling (or freezing) of 6.

magma. Do you think all minerals form from in this manner? If not, think of an

example of another way a mineral could form.

Quartz (SiO2) is a very common mineral but large 7.

well-formed crystals, like the one pictured at right are

relatively rare. Describe a possible scenario in which

a well-formed crystal like this one could form.

Pixabay Pubic Domain

Name:_______________________________________________________ Date:______


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Background Reading Part II: Mineral Identification

Goals: Our goal in this lab is to become familiar with common physical properties of rock forming minerals and learn some basic techniques of mineral identification.

Background: Each mineral is characterized by a specific chemistry and internal structure. As a

result, all specimens of a particular mineral will possess diagnostic physical properties. The

physical properties of minerals we will investigate are: Cleavage, Hardness, Color, Density,

Luster, and Reaction to Hydrochloric Acid. Other properties you might consider are Crystal Form, Taste, Magnetism, Streak, and Optical Properties.

You will only be responsible for the following common rock forming minerals on the lab exam:

Quartz, Potassium Feldspar, Plagioclase Feldspar (light and dark), Muscovite, Biotite,

Amphibole (Hornblende), Pyroxene (Augite), Olivine, Calcite, Halite, Gypsum, Galena, and

Pyrite.

The following includes some additional information that will help with understanding the

differences and similarities of these minerals. Remember we are focusing on some of the

most common minerals found in the earth’s crust (other than galena).

Quartz.

Quartz can occur as either visible crystals or as aggregates of very small crystals.

Quartz often endures the earth’s erosive processes because it is hard and lacks cleavage.

This hardness allows it to be polished (by nature or rock tumblers) and is one of the reason it is often used as a gemstone.

Small impurities of other elements can give quartz different colors, bands, or patterns.

Much of the cryptocrystalline quartz (agate, chert, etc.) forms when silicon dioxide

crystallizes (precipitates) from groundwater.

Feldspar. Feldspars are a very common mineral in igneous rocks. However, their excellent

cleavage and chemistry cause them to easily weather to clays. Therefore they are not as common away from their source areas (such as large granite outcrops) as quartz.

Feldspar is a mineral group that includes Potassium Feldspar and Plagioclase Feldspars.

The Plagioclase Feldspars are a subgroup of feldspars that range from light-colored

Albite (sodium-rich) to dark-colored Anorthite (calcium-rich).

Plagioclase can sometimes be distinguished from the Potassium Feldspars by the

existence of striations (fine parallel grooves on the mineral surface).

Micas- This includes both Muscovite and Biotite that have similar hardness and cleavage

Amphibole and Pyroxene – These are both dark minerals with similar hardness. The cleavages on these minerals can be difficult to determine, but amphibole does not have 90 degree cleavages

and Pyroxene does have 90 degree cleavages. This can be used to distinguish the two.

Aggregates – some of our specimens occur as aggregates of very small crystals (olivine and

pyrite). Consequently it may be difficult to determine hardness and cleavage for these

specimens.

26

Moh’s Scale of Hardness

Moh’s Scale and Minerals Hardness of Common

Objects

10 – Diamond

9 – Corundum

8 – Topaz

7 – Quartz

6 – K-Feldspar (orthoclase)

5 – Apatite

4 – Fluorite

3 – Calcite

2 – Gypsum

1 - Talc

6.5- Streak Plate

5. 5 – Glass, Knife Blade

4.5 – wire, iron nail

3.5 – penny

2.5 - fingernail

Fracture and Cleavage – light reflection

Fracture – light is scattered

by irregular surfaces

Perfect Cleavage – flat

surface reflects all light in

the same direction

Multiple Cleavage surfaces

reflect light in the same

direction to produce a

“flash” when the specimen

is turned in the light

Number of Cleavages Description Diagram

0 Irregular Masses without

shiney surfaces

1 Basal - “books” split apart

along the base

2 @90 Prisms – rectancular

sections

2 not @90 Prisms without right angles

3 @ 90 Cubic

3 not @ 90 Rhombic Cleavage – look

like skewed cubes

Name:_______________________________________________________ Date:______


27

Lab 3.2: Known Minerals Task: Investigate the lab specimens to complete the mineral property chart below and indicate the most diagnostic properties for each mineral.

Mineral Properties

Name Silicate or

Nonsilicate

Hardness Cleavage (number

and angles); or

Fracture

Color Other: Unique Density, Streak, Acid

Reaction, Metallic Luster

Quartz

Muscovite

Biotite

K-Feldspar (Orthoclase)

Na-Plagioclase Feldspar

Ca-Plagioclase Feldspar

Amphibole

(variety Hornblende)

Pyroxene

(variety Augite)

Olivine

Calcite

Gypsum

Halite

Pyrite

Galena

28

Lab 3.3: Unknowns

Identify the unknown mineral samples and state the distinguishing properties that were

most helpful to you in identifying the mineral.

Specimen Mineral Name Key Properties

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

Identify the minerals present in the provided rock samples:

Rock 1 Rock 2 Rock 3 Rock 4 Rock 5

Name:_______________________________________________________ Date:______


29

Lab 3.4: Special Minerals

Investigate at least two of the “Additional Minerals” provided. DO NOT scratch these

minerals or apply acid. Please treat them gently. You can use the reference material

provided to answer the questions.

For each mineral indicate:

1. Describe the mineral color and other visual appearances

2. Describe the mineral shape (e.g., bladed, cubic, columns, hexagonal, etc)

Use the references to answer the following:

3. Hardness and specific gravity (or density), distinguishing features

4. List the formula for the mineral

5. Indicate if the mineral is a silicate or a non-silicate.

6. If it is a non-silicate, indicate the specific mineral class (e.g., oxide, halide,

etc.)

7. Briefly describe the environment of formation

Mineral: Mineral:

1 1

2 2

3 3

4 4

5 5

6 6

7 7

30

Minerals Quiz Review Sheet

Examples of Questions:

Describe the distinguishing properties of the mineral in this aggregate

List the mineral name

Describe, as completely as possible, the cleavage of this mineral

Describe the hardness of this mineral (this is not a mineral we saw in the lab)

List a property that allows you to distinguish this mineral from others we have

examined in the lab.

List two of the minerals present in this rock

List the hardness of this mineral

You are responsible for the following mineral properties:

Color

Streak

Hardness

Cleavage Planes and Angles (or fracture)

Acid Reaction

Density

Distinguishing Properties (how you tell this mineral from one that may be similar)

You are responsible for identifying the following minerals:

Quartz, Muscovite, Biotite, Potassium Feldspar, Sodium Plagioclase Feldspar,

Calcium Plagioclase Feldspar, Amphibole (hornblende), Pyroxene (augite/hypersthene),

Olivine

Calcite, Halite, Gypsum, Pyrite, Galena

Notes: You can use one side of 8.5x11 paper with your own notes – typed or hand

written.

NOT ALLOWED:

Any of the tables or charts in this lab book unless you type or write it onto a new

sheet.

Photocopies or scans of the lab, book, or another student’s work]

Photographs of minerals

Consulting experts or other students during the exam

Photographs of our lab samples are available using the following link:

http://tinyurl.com/g1mineral This link will also be available through Canvas. You will

also have time to study the samples in the lab.

http://tinyurl.com/g1mineral

Name:_______________________________________________________ Date:______


31

Lesson Four: Igneous Rocks

Background Reading: Igneous Rocks

Igneous Rocks: Cool (crystallize) from a magma

There are two main types of Igneous Rocks:

A. Intrusive or Plutonic

B. Extrusive or Volcanic

Igneous Rocks are defined by Texture and Composition

I. Igneous Textures: Crystal Size

Crystal size is determined by the rate of cooling.

Slow cooling results in larger crystals.

Fast cooling results in smaller crystals.

Glass consists of unordered ions (and is therefore not crystalline). This can be the

result of either extremely fast cooling or from a high silica content that prevents ions

from bonding to form a crystalline structure.

Aphanitic (fine-grained texture) – from fast cooling. Found in volcanic rocks.

Phaneritic (coarse-grained texture) –from slow cooling. Found in plutonic rocks

Porphyritic: Larger crystals embedded in a matrix of smaller crystals. The larger

crystals are called phenocrysts.

The term porphyritic is often used to describe volcanic rocks. However it is

sometimes used to describe plutonic rocks if much larger crystals are embedded within

a coarse-grained rock).

II. Igneous Composition:

Basic Subdivision of Felsic and Mafic

Felsic: rocks that include substantial amounts of feldspar (fel) and quartz (si). Felsic

rocks have a composition close to granite. Felsic rocks have abundant quartz,

potassium and sodium feldspars (Na-plagioclase), and muscovite, with lesser amounts

of biotite, and amphibole.

Mafic: rocks include substantial amounts of Iron and Magnesium bearing minerals

(MgFe=mafic). Mafic rocks have a mineral assemblage close to basalt. Mafic rocks

include Calcium-rich feldspar (Ca-plagioclase), pyroxene, amphibole, and olivine (but

little or no quartz).

III. Generation of Magma

Rock near their melting points will melt if a) the pressure drops, or if b) volatiles

(including water) are added.

Water acts like salt does to ice. That is, it lowers the melting temperature of the

material. Water added from plate subduction lowers the mantle rock melting

temperature. This causes the mantle rock to melt, which then rises and heats crustal

rocks to their melting point.

32

IV. Fractional Crystallization – the process of progressive crystal formation.

This results in progressive extraction of iron, magnesium, calcium and other elements

from a magma, so the remaining magma becomes more felsic (richer in silica, sodium,

and potassium).

How magmas change during cooling. Bowen’s reaction series shows the

crystallization temperatures for minerals.

Bowen’s Reaction Series explains the sequence of crystallization from a magma, and

it provides a mechanism to explain how the composition of magma changes during

cooling.

Bowen’s Reaction Series

A list of minerals arranged in the order of the temperature at which they crystallize

(or melt).

Mafic (dark) minerals crystallize at higher temperatures than felsic (light) minerals.

If cooling is slow and required elements present, early formed minerals will react

with the remaining liquid to form new minerals (lower on the list).

The final rock composition depends on the initial composition of the magma.

Example: if a mafic magma cools, then olivine, pyroxene, Ca-plagioclase, and

amphibole will crystallize and all the magma will be gone. If a felsic magma cools,

then there may not be enough iron and magnesium to form olivine or early-formed

olivine will react to eventually form amphibole.

Who cares?

This tells us that we will expect to find dark minerals together and light minerals

together (grouping of minerals higher and lower on the list).

This explains how we can get a variety of rock types from the same initial magma

(crystal settling or magma separation).

This explains how we can get a less mafic magma (more felsic) by a process of mafic

rocks forming and enriching the magma in more felsic material.

Name:_______________________________________________________ Date:______


33

Figure Credit: Bob McPherson, used by permission

34

Clasification of major groups of igneous rocks based on mineral composition and textures

Chemical Composition Felsic (silicic) Intermediate Mafic Ultramafic

Dominant Minerals Quartz

Potassium (K) – Feldspar

Sodium (Na) - Plagioclase

Amphibole

Sodium (Na) – Plagioclase

Calcium (Ca) - Plagioclase

Pyroxene

Calcium (Ca) - Plagioclase

Olivine

Pyroxene

Accessory Minerals Muscovite

Biotite

Amphibole

Pyroxene

Biotite

Amphibole

Olivine

Calcium (Ca) -

Plagioclase

Color/Shade

Lighter color Intermediate Color Dark Color

(salt and pepper)

Volcanic (Extrusive) Aphanitic or Aphanitic-porphyritic textures

Rhyolite Andesite Basalt Uncommon

Plutonic (Intrusive) Phaneritic or Phaneritic-

Porphyritic textures

Granite Diorite Gabbro Peridotite

Glassy Textures

Vesicular Glass = Pumice (light) or Scoria (dark). Compact Glass = Obsidian

Pyroclastic

(Fragmental) Textures

Pyroclastic Volcanic Rocks: Ashy with pumice fragments = Tuff. Large Angular Fragments = Volcanic Breccia

Name:_______________________________________________________ Date:______


35

Worksheet 4.1: Igneous Rocks

Use the diagram above to identify features that are intrusive and extrusive. Fill 1.

our the chart below with the names of the features labeled in the diagram.

Intrusive Features Extrusive Features

Indify the specific locations (labeled on the diagram) where large, medium and 2.

small crystals would form.

Largest Crystals Medium Crystals Small Crystals

36

(Multiple Choice) How do most intrusive igneous rocks reach the surface of the 3.

earth for geologist to study?

a. They are erupted from volcanoes

b. They are mined

c. Millions of years of uplift and erosion of overlying material expose them

at the surface

d. They are found almost entirely in the deepest river canyons such as the

inner gorge of the Grand Canyon where rivers have cut into the deep crust

Use the Bowen’s Reaction Series diagram on pg. 32 to Identify each of the 4.

following minerals as either mafic (M), felsic (F), or Intermediate (I).

Olivine_____ Muscovite ______

Quartz_____ Calcium-Rich Feldspar _____

Potassium-Rich Feldspar ____ Amphibole ______

Pyroxene _____ Sodium-Rich Feldspar _____

Biotite _____

Use the Igneous Rock Identification Chart on pg. 34 to determine the 5.

appropriate name for each of the following rock descriptions.

Description Rock Name

A dark colored rock found in a lava flow

An intermediate, phaneritic rock

The volcanic equivalent of granite

A rock that contains visible crystals of quartz, potassium

feldspar, sodium plagioclase feldspar and small amounts

of biotite and amphibole

A rock that contains some visible crystals, surrounded

by a dull colored, fine grained groundmass. The

abundant visible crystals (phenocrysts) can be identified

as amphibole.

Consider a sample of basalt with large olivine crystals (phenocrysts). 6.

a. Explain how this association (basalt and larger olivine crystals) formed.

b. Explain if this association is consistent (or inconsistent) with Bowen’s

Reaction Series.

Name:_______________________________________________________ Date:______


37

Consider a solid piece of Diorite that is made of the minerals Plagioclase 7.

Feldspar, Amphibole, and small amounts of quartz, muscovite, and biotite. If

you slowly heat this rock, what are the first minerals that would melt, according

to Bowen’s Reaction Series?

The Fantastic Lava Beds in Lassen National Park are basaltic andesite to 8.

andesite in composition but contain visible crystals of quartz. Is this association

consistent or inconsistent with Bowen’s Reaction Series? Explain.

Some of the granite in the Pikes Peak Batholith in Colorado contains a small 9.

amount of a variety of olivine. Is this association consistent or inconsistent with

Bowen’s Reaction Series? Explain.

38

Lab 4.2: Igneous Knowns

Complete the following chart. Determining the minerals for aphanitic rocks may not be possible. In those cases either state none

observed (NO) or list the color and the nature of any phenocrysts.

Color (light, med., dark)

Minerals Observed

(list only those that can actually be observed)

Composition

(Mafic, Intermediate, Felsic)

General Texture

(Phaneritic, Aphanitic, Porphyritic-Phaneritic,

Porphyritic-Aphanitic)

Special

VolcanicTextures (Glassy, Vesicular,

Pyroclastic)

Specimen A (Granite)

Specimen B (Rhyolite)

Specimen C (Diorite)

Specimen D (Andesite)

Specimen E (Gabbro)

Specimen F (Basalt)

Specimen G (Peridotite)

Specimen H (Obsidian)

Specimen I (Pumice)

Specimen J (Scoria)

Specimen K (Tuff

and/or Volcanic

Breccia)

Name:_______________________________________________________ Date:______


39

Lab 4.3: Igneous Rock Unknowns

Determine the igneous rock properties for each of the unknowns. Only list minerals you actually observed

Specimen Color (light, med., dark)

Minerals Observed (list only those that can

actually be observed)

Composition (Mafic,

Intermediate,

Felsic)

General Texture (Phaneritic, Aphanitic,

Porphyritic-Phaneritic,

Porphyritic-Aphanitic)

Special

VolcanicTextures

(Glassy, Vesicular,

Pyroclastic)

Rock Name

A

B

C

D

E

F

G

40

Specimen Color

(light, med., dark) Minerals Observed

(list only those that can

actually be observed)

Composition

(Mafic,

Intermediate, Felsic)

General Texture

(Phaneritic, Aphanitic,

Porphyritic-Phaneritic, Porphyritic-Aphanitic)

Special

VolcanicTextures

(Glassy, Vesicular, Pyroclastic)

Rock Name

H

I

J

K

L

M

N

Name:_______________________________________________________ Date:______


41

Igneous Rock Lab Quiz – Review Sheet

You are responsible for identifying the following rocks

Rhyolite

Andesite

Basalt

Granite

Diorite

Gabbro

Peridotite

Obsidian

Pumice

Scoria

Volcanic Breccia

Volcanic Tuff

You are responsible for identifying distinctive minerals in intrusive igneous rocks

and phenocrysts in extrusive igneous rocks: Quartz, K-feldspar, Muscovite, Biotite,

Na-Plagioclase, Ca-Plagioclase, Amphibole, Pyroxene, Olivine, and possibly one of the

more common non-silicate minerals (calcite, pyrite)

You are responsible for identifying and explaining the formation of the following

textures

Phaneritic, Phaneritic-Porphyritic

Aphanitic, Aphanitic-Porphyritic

Glassy

Pyroclastic

Vesicular

Sample Questions

Describe (and name) one of the minerals in this rock that can be used to justify the

rock name., and List the rock name

Describe (and name) one of the visible minerals in this rock that can be used to

justify the rock name.

List the texture of this igneous texture and describe how it formed

Both samples provided are classified as the same specific igneous rock type.

Identify this rock

Notes: You can use one side of 8.5x11 paper – typed or hand written. You are not

allowed to use the lab sheets and table from this packet.

NOT ALLOWED:

The lab tables unless you type or write it onto a new sheet.

Photocopies or scans of the lab, book, or another student’s work.

Photographs of minerals

Consulting experts or other students during the exam

Photos of igneous rocks are available on the Canvas course page and at the following

URL: http://tinyurl.com/g1igneous

http://tinyurl.com/g1igneous

Name:_______________________________________________________ Date:______


43

Lesson Five: Volcanoes Background Reading: Volcanoes

Volcanic Terms:

Silca: SiO2 – silicon dioxide. This is quartz when it crystallizes. The amount of this in

the magma determines the viscosity (thickness) of the magma.

Viscosity: resistance to flowing. A more viscous magma is “thicker” in the same way

that honey is thicker than water. The more viscous a magma, the greater its ability to trap

gas and produce an explosive eruption. If it is too viscous (like obsidian or even rhyolite

magma), it may be too thick to erupt and it will form domes and plugs.

Pyroclastic material: hot fragments blown out of a volcano. It can range from very

small ash to much larger fragments (lapilli, bombs). Pyroclastic material can be ejected

upward, or flow down a volcano (pyroclastic flow) as a extremely hot avalanche of

pyroclastic debris.

Stratovolcano: A large, cone-shaped volcanoes consisting of alternative layers of lava

and pyroclastic material. Mt Shasta and Mt Rainier are stratovolcanoes. These

volcanoes are often associated with convergent plate boundaries and explosive eruptions.

Shield Volcanoes: A volcano with a broad, gentle-sloping dome formed from low

viscosity basaltic lava. These volcanoes exhibit Effusive eruptions. These are not violent

eruptions. Lava pours out onto the ground from a vent and spreads out over the land.

Three main types of volcanic rock types and associated volcanism:

Rhylolite: highest silica content (other than obsidian); it is the most viscous of all lavas;

it’s viscosity causes it to form domes or freeze while still in the volcanic vent.

Andesite: intermediate silica content; its relative “thickness” (viscosity) causes gas to

build up pressure within the magma and result in explosive eruptions. The flows are

relatively short, but extensive pyroclastic material can be produced. Andesitie volcanism

can form stratovolcanoes.

Basalt: low silica content; it is the least viscous of the lavas and consequently it tends to

create large flows and less explosive eruptions. This ability to flow also results in shield

volcanoes with low-sloping sides due to the runoff of lava. The flows can cool to

produce columnar jointing and the more fluid lava will cool to form a ropey appearance

(pahoehoe lava).

Plate Settings and Volcanism

Divergent Boundary: typically divergent boundaries are sites of basaltic volcanism.

This is true of the oceanic ridges. Pillow basalts form as the submarine lavas at mid-

ocean ridges cool. The initial stages of continental plate divergence can result in more

silica-rich volcanism, due to the silica-rich nature of the continental crust.

Convergent Boundary: Convergent plate boundary volcanism can be complex. It

typically produces andesitic lavas and this results in formation of stratovolcanoes.

However, basaltic volcanism is also common at convergent boundaries. The Cascade

Volcanic Chain is an example of the variety of volcanism present at a convergent

boundary. The Cascade chain includes stratovolcanoes, shield volcanoes, pyroclastic

deposits, and obsidian domes.

Hot Spots: (Oceanic-basalt or Continental-rhyolite): This can be anywhere in the

lithosphere. If they occur within oceanic crust (like Hawaii), they produce basalt

44

volcanism and shield volcanoes. If they occur within continental crust they can be silica

rich and produce very explosive volcanoes such as the Yellowstone Caldera.

Geologic Hazards / Risk

Lava Flows – most only travel a few meters per hour and are slow enough for

people to get out of the way.

Pyroclastic Hazards;

o Ash falls

o Lateral blast

o Pyroclastic flows -ash flow (very fast and burns up everything in its path)

Poisonous Gas - H20, C02, S02 - suffocation

Lahars / Mudslides

o Related to rapidly melted snow/ice

o Flow rates: volcano base= up to 40 meters/second

o 1Km out on plain = up to 10 meters/second

o May be triggered by earthquakes, storms, gravity, volcanic eruptions

o Travel Rapidly, may be little advance warning.

Prediction of Volcanic Eruptions seismic activity - earthquakes

thermal, gravity, magnetic, electrical changes

tilting or swelling (ground level change)

gas emissions

historical information

rock type - silica rich or not?

Usually days to hours of notice. Size and direction of blast are harder to predict.

Preparation

Identify Potentially Hazardous Volcanoes

o Plate Boundaries

o Past History - Dating of Deposits

o Current Status - Predictors

Identify Nature of Hazard

o Rock Type - How Explosive

o Other Hazards - Lahars, Poisonous Gas

Education, Zoning, Evacuation Plans

Continued Monitoring

Name:_______________________________________________________ Date:______


45

Magma Types and Volcanic Landforms

Composition Silica Content Viscosity

Tendency for

Pyroclastic

(explosiveness)

Volcano Type; Volcanic

Landform

Mafic

Basaltic Magma 50% = low Low Least

Shield Volcano

Basalt Plateau (Flood Basalt)

Cinder Cone

Underwater Fissure

Intermediate

Andesitic Magma

60% =

intermediate Intermediate Intermediate

Composite Volcano (Stratovolcano)

Volcanic Domes

Felsic (Silicic)

Rhyolite Magma

70% or greater

= high High Greatest

Volcanic Domes (Obsidian)

Calderas (Supervolcanoes)

Types of Volcanoes

Low

Viscosity

High

Viscosity

Volcano Type Characteristics Examples

Flood Basalt;

Basalt Plateau

Very fluid basaltic lava;

Widespread flows emitted from

fissures

Columbia River Plateau

Deccan Plateau (India)

Shield Volcano

Basalt lava forming a shallow-

sided cone

Hawaiian Volcanoes;

Medicine Mountain Volcano

Underwater

Fissure

Basalt erupts in the deep ocean.

The presence of water creates small explosions as the water is

vaporized. New oceanic crust is

formed.

Mid Atlantic Ridge East Pacific Rise

West Mata Volcano

Cinder Cone

Explosive pyroclastic eruptions;

small, steep-sided cone; sometimes

associated with Shield Volcanoes.

Paricutin (Mexico);

Numerous cones in Lava Beds

National Monument; Red Mountain (Arizona)

Composite

Volcano (or

Stratovolcano)

More viscous lava (usually

andesitic); steep-sided large cone;

eruptions include lava flows as well

as more explosive pyroclastic

eruptions, including small

pyroclastic flows.

Mount Shasta

Mount Rainier

Mount Saint Helens

Volcanic Domes

or Plugs

Very viscous lava (may be volcanic

glass); generally, small and

associated with calderas or

composite volcanoes.

Mount St. Helens Lava Domes; Mono Craters

Caldera from a

Caldera

Eruption

Very large volcano explosion and collapse; very large pyroclastic

flows.

Yellowstone Long Valley

Mt. Mazama (Crater Lake)

Tables: Bazard and Wright, 2017

46

Worksheet 5.1: Volcanoes

Mt. Hood in Oregon is a composite volcano. If you were to hike up Mt.Hood, what 1.

type of rock would you expect to find most often when you stop to observe outcrops

along your way?

Last summer, I visited an obsidian flow in the Newberry Caldera in Central Oregon. 2.

What is the composition of the magma that produced this flow?

The Big Island of Hawaii is composed of multiple Shield Volcanoes, describe the 3.

appearance (color, texture, phenocrysts) of rocks that you would find in Hawaii.

Describe the type of volcano that would be expected at each of the following settings. 4.

a. A hot spot located in the middle of an oceanic plate.

b. A convergent plate boundary with an oceanic plate subducting beneath a

continental plate.

c. A hot spot within a continental plate.

Name:_______________________________________________________ Date:______


47

Label at least one dike and at least one sill in the cross section below.5.

Refer to the image below showing potential volcanic hazards. What type of volcano 6.

is pictured and how can you tell?

USGS Public Domain

48

Study the volcanic hazard map above. This map shows the hazards associated with 7.

an eruption of Mt. Rainier. Note that Seattle is located just off the map to the north of

Tacoma. Which of these hazards do you think is most concerning to public officials

in Washington State? Why?

Modified from USGS public domain map

Name:_______________________________________________________ Date:______


49

Lesson Six: Weathering and Sedimentary Rocks Background Reading: Sedimentary Processes

The formation of sedimentary rocks is the result of several processes. The fundamental processes are weathering of pre-existing rocks, transport of sediment, deposition of sediment, and finally

cementation and other processes that occur after deposition (this is called diagenesis). This

progression is shown below.

Weathering Transport

Deposition

Cementation / Diagenesis

Weathering The process begins with weathering. Weathering consists of both mechanical weathering (or

sometimes called physical weathering) and chemical weathering. Mechanical weathering breaks

rocks down into pieces that then provide more surface for chemicals to attack. Thus, mechanical weathering speeds up the weathering processes by providing more surfaces for the chemical to

attack.

Mechanical Weathering Examples of mechanical weathering are provided in Worksheet 6.1on page 54.

Chemical Weathering Oxidation – reaction with oxygen – rust (hematite, limonite) Solution – dissolving of minerals and release of ions; example: salt (halite) dissolving in

water

Hydrolysis– chemical reactions that produce clay minerals

Chemical weathering is aided by the presence of Carbonic acid in rainwater and

groundwater.

CO2 in atmosphere and soil dissolves in water to form carbonic acid:

Carbonic acid will dissolve calcite (CaCO3) to release calcium into solution. It can also

aid in weathering feldspars and other minerals. Many minerals weather to clay and release ions: For example, Potassium Feldspar reacts

with Carbonic Acid to produce Kaolinite clay, potassium, and silica

Quartz is very stable and does not easily weather due to chemical (or mechanical)

processes.

50

Transport: Mechanisms of sediment transport include Rivers, Wind, Glaciers, Gravity,Waves Weathering continues during transport. Other important processes also occur during transport.

These processes include:

Rounding – This is related to length and mechanism of transport

Transport by rives, waves, and wind cause rounding. There is less rounding with short transport and with glacier transport.

Angularity and sphericity are described in the textbook. These are similar in concept to the

idea of evaluating grains by how they have been smoothed and eroded during transport. However, we will keep things simple and only consider rounding in our discussion of how

grains mechanically change during transport.

Sorting- is the degree to which grains are similar in size Sorting is related to length of transport. Longer transport generally results in better sorting.

In general, the size of grains deposited is related to the energy of transport. This is a key concept

and something we will use in evaluating depositional environment (described below).

Therefore, large grains are the only grains that will be deposited in rapidly moving water,

and small grains are deposited in slow moving water after all of the larger moving grains have already been deposited (upstream in faster moving water). Small grains are deposited

in areas such as bays, lakes, or the open ocean, where the transport energy is low.

Wind and river transport is often an effective method of sorting. Glacial transport is often a poor means of sorting (the exception being the stream transport at the end of a glacier).

Deposition: deposition occurs when transport stops. Depositional Environments are described as: The geographic setting where sediment accumulates.

We will consider three main types of depositional environments:

1. Terrestrial (Nonmarine). This is sometimes called continental, 2. Marine,

3. Transitional (shoreline)

These types can then be subdivided by considering the energy of the setting: low, medium, high energy and specific conditions (rivers, dunes, glaciers)

Example of a depositional environment: A mountain steam is a medium to high energy terrestrial

depositional environment.

In general, rivers represent several depositional environments depending on the energy of each

environment within the river. For example, we would expect larger grains to be deposited in the high-energy channel environment and small grains (silt or clay) to be deposited in the low-energy

environment of the river banks or floodplain.

Post-depositional changes: Diagenesis Diagenesis is a collective term for all of the chemical, physical and biological changes that take place after deposition

Lithification: an important diagenetic process that includes compaction and cementation to form

a hardened sedimentary rock. The cementing agents produced include: quartz, calcite, hematite

(iron oxides)

Oxidation: oxidation of iron-bearing minerals in the rock give a common red/orange

color.

Name:_______________________________________________________ Date:______


51

Sedimentary Rocks

Sedimentary rocks are formed in two general ways. Clastic sedimentary rocks are formed when

sediments are deposited, compacted, and cemented. Chemical and biochemical sedimentary

rocks are formed when minerals precipitate from water, or when minerals precipitated by an

organism are cemented together.

Clastic sedimentary rocks are characterized by the size, shape, and (for coarse-grained rocks) the

composition of the clasts. The clasts sizes are divided into the following categories:

Gravel to Boulder size: >2mm Sand Size: 0.0625mm-2mm (you can see most sand sized grains)

Silt Size: 0.004mm-0.0625mm (grains cannot easily be seen, but feels “gritty”)

Clay Size: <0.004mm (feels smooth and powdery)

Clastic Sedimentary Rock Names

Conglomerate is made mostly of rounded gravel- to boulder-sized clasts. (most of the grains are

larger than sand size) Breccia is made mostly of angular gravel- to boulder-sized clasts. (most of the grains are larger

than sand size)

Sandstones are made mostly of sand-sized clasts. These rocks are classified based on the composition of grains and the amount and type of material between the grains. They are also

described in terms of rounding and sorting of grains.

Quartz-Rich Sandstone (or Arenite) is made of almost all quartz grains with a quartz cement.

Wacke Sandstone (or Graywacke) has a variety of grain types and mud between grains. This is a common sandstone in Humboldt County. You can think of this as a “dirty” sandstone.

Arkose Sandstone contains abundant feldspar. These rocks are common near exposed

granite. Note: (We will not be using Lithic Sandstone, which is described in the textbook).

Siltstone and Claystone are formed from cemented silt or clay clasts.

Mudstone is composed of both clay and silt. Shale is either Siltstones or Mudstone with distinctive, thin layers or partings.

Chemical and Biochemical rocks are characterized by specific minerals.

Common minerals in Chemical Sedimentary Rocks: Halite, Gypsum, Calcite, and Silica (quartz) can precipitate from water.

Crystalline Limestone is formed by precipitation of calcite from water.

Fossiliferous Limestone is formed from the accumulation of calcite-rich organic fragments (shells).

Muddy Limestone (Micrite) looks similar to mudstone, but the mudstone is calcite rich

Chalk – powdery calcite-rich rock formed from the accumulation of microscopic calcite forming organisms – this one reacts to hydrochloric acid.

Clastic Limestone is a clastic rock (formed of grains), but the grains are calcite rich

Chert is formed either out of solution (from silica rich water), or from accumulation of organic

fragments (very small silica-rich shells). Diatomite – powdery silica-rich rock formed from the accumulation of one-celled diatoms.

Evaporites: Salt (halite) and Gypsum deposits are formed as water evaporates.

52

Textural Features of Sedimentary Rocks

Grain Sizes Grain Shapes Grain Arrangements

Gravel Size and Larger

greater than 2 mm

Sand Sizes Ranges from Very-Coarse to

Very-Fine Grained Sand

2mm to 1/16 mm

Grains can be seen with the

unaided eye.

Silt Sizes 1/16mm to 1/250mm

(.0625 - .004mm)

Grains not visible, but feel

“gritty”

Clay Sizes Less than 1/256mm,

(<0.004mm)

Grains not visible, feels smooth.

Grains cannot be seen with a

common microscope Images: Bazard, 2012 and Public Domain

Name:_______________________________________________________ Date:______


53

Sedimentary Rock Classification Chart

Clastic Sedimentary Rocks Chemical / Biochemical Sedimentary Rocks

Grain Size Calcite-Rich Rocks Silica-Rich Rocks

>2mm

(granule to boulders)

Breccia (angular grains)

Conglomerate (rounded grains)

Crystalline Limestone

Fossil-Rich Limestone

Mud-Rich Limestone (Micrite)

Chalk (powdery limestone)

Chert (includes flint, jasper,

chalcedony, agate)

Diatomite (powdery, silica-

rich, from diatoms)

2mm-1/16mm

(very-coarse to very-fine

grained sand)

Sandstones:

Quartz-Rich Sandstone (Arenite)

Feldspar-Rich Sandstone (Arkose)

Mud-Rich Sandstone (Graywacke)

Less than 1/16mm

(includes silt and clay)

Grains not seen

Rocks range from

gritty (silt content) to

smooth (clay rich)

Mudstone (massive)

Shale (finely layered silt and clay)

Rocks Made of Evaporite Minerals

Halite – Rock Salt

Rock Gypsum

54

Worksheet 6.1: Sediment

Weathering is the breakdown of rocks at the surface of the earth.

Mechanical (or physical) weathering results as force or pressure is applied to a rock

resulting in fracture into smaller rock fragments that retain their chemical composition.

Chemical weathering results from chemical reactions that break down the minerals within

the rock at a molecular level.

1. Characterized each of the weathering processes in the list below as either mechanical

or chemical by writing an M or a C next to the process

a. A rust colored band appears along an existing crack in a rock.

b. Exfoliation (pressure release fracturing)

c. Frost wedging

d. Tree root wedging

e. Lichen growth (a moss-like organism that lives on the surface of rocks)

f. Putting HCl on a calcite sample in lab

g. The deterioration of the gargoyles on the Notre Dame

h. Abrasion (sediment is rubbed against a rock)

i. Gravel in soil breaks down into clay

j. Salt wedging (in coastal areas salt crystals grow in cracks in rocks,

expanding and breaking the rocks)

2. Consider the chemical weathering of granite. Use the table below to identify the

minerals that will remain after complete weathering.

Products of Weathering

Mineral Residual Products

(minerals)

Material in Solution

(Ions)

Quartz

Quartz Grains

(Quartz does not chemically

weather easily)

Silica

Feldspars (K, Na, Ca)

Clay Minerals Silica, K, Na, Ca

Micas (Biotite, Muscovite) Clay Minerals

Iron-Oxide Minerals

Silica, K, Mg

Amphibole

Clay Minerals, Iron-Oxide Minerals

Silica, Ca, Mg

Olivine and Pyroxne

Clay Minerals,

Iron-Oxide Minerals

Silica, Mg

Name:_______________________________________________________ Date:______


55

3. For each of the following characteristics, identify whether the characteristic

generally increases or decreases with transport time. (Write I or D next to the

characteristic)

a. Grain size

b. Grain sorting

c. Grain rounding

d. Percent Feldspar

e. Percent Quartz

4. Organize the list of depositional environments based on the energy of the

depositional environment:

Sandy ocean beach

Windblown desert

Lake bottom

Glacier

Flooding mountain stream

River floodplain

Energy Depositional Environment Maximum Grain

Size

High

Energy

Low

Energy

5. Complete the Maximum Grain Size column in the table above with grain size

terms such as “boulder” or “fine sand”

56

6. Below is a list of descriptions of sedimentary rock units and a list of specific

depositional environments. Match the correct depositional environment with the

rock that most likely formed in that environment. (Note: There may be one trick

question in this)

Rock 1: Poorly sorted, angular, arkosic conglomerate. Contains many granite rock fragments.

Pink to dark red in color.

Rock 2: Well sorted, well rounded, medium grained quartz sandstone. Tan to gray in color.

Rock 3: Well sorted, well rounded, fine grained quartz sandstone. Pink to red in color.

Rock 4: Fine grained limestone containing abundant marine fossils.

Rock 5: Mudstone and shale with layers of evaporite minerals such as halite and gypsum.

Depositional Environments: Continental Shelf: The ocean, well past the tidal zone, but still within the continental crust.

Desert Dunes: Very large dunes, some up to 100 meters high. Similar to the Sahara.

Alluvial Fan: A fan shaped deposit of sediment at the base of a mountain range, where mountain

streams flow into flat valleys. These are common in Death Valley.

Ocean Beach: You know, a beach.

Playa Lake: A shallow lake in a desert valley that sometimes dries completely.

Rock Depositional Environment

1

2

3

4

5

7. The sketch below shows a cross section view of cross bedding. Label the bedding

and the cross bedding and add an arrow showing the direction of current flow.

Name:_______________________________________________________ Date:______


57

Lab 6.2: Analyzing Sediment

Exercise #1: Analyze the sediment sample(s) provided and describe the rounding and

sorting of the sample

Exercise #2: Make a grain size card.

Use the Sieve to separate the sediment into different grain sizes.

Glue a small portion of each grain size onto a single card and label the sizes (use terms

such as larger than sand, coarse sand, fine sand, etc.)

Exercise #3: Decomposed Rock Sample

Clastic sedimentary rocks may include fragments of pre-existing rocks.

A. List the minerals you can identify in these rock fragments?

B. What was the pre-existing rock?

C. Are there any products of chemical weathering present? If so what are they?

Exercise #4 Sandstones

For each of the sandstones describe: Graing Size Range: The smallest grain size and the largest grain size present (e.g. silt to granule)

Median Grain Size: estimate that average grain size (what size are most of the grains) Grain Sorting and Grain Rounding

Grain Composition: In particular is there quartz, feldspar or mud (silt and clay) present

Cement: If possible identify the mineral that composes the cement

Rock Name (e.g. Arkose)

Grain

Size

Range

Median

grain size

Grain

Sorting

Grain

Rounding

Grain

composition

Cement Rock

Name

A

B

C

58

Lab 6.3: Sedimentary Knowns

Use the labeled samples provided to answer these questions

Look at the specimens and answer the questions below.

Rock Set 1:

How can one distinguish Breccia from Conglomerate?

Rock Set 2:

How can one distinguish Sandstone from Mudstone (or shale)?

Rock Set 3:

How can one distinguish Fossiliferous Limestone from Crystalline Limestone?

Rock Set 4:

How can one distinguish Micrite (muddy limestone) from Chert?

How can one distinguish Micrite from Mudstone?

How can one distinguish Mudstone from Shale?

Rock Set 5:

How can one distinguish a Quartz-Rich Sandstone from Graywacke Sandstone?

How can one distinguish an Arkose Sandstone from a Quartz-rich Sandstone?

Rock Set 6:

How does Diatomite differ from Chalk?

Name:_______________________________________________________ Date:______


59

Lab 6.4: Sedimentary Unknowns:

* These properties may not apply to all specimens and in some cases they may be left blank.

Clastic or

Chem/BioChem?

Grain Size

(for Clastic)*

Grain Rounding and

Sorting

(for Clastic)*

Grain composition

(for Clastic)*

Cement (clastic) or

Mineral (chem)

Composition

Acid

Test

Fossils Name

A

B

C

D

E

F

G

60

Clastic or

Chem/BioChem?

Grain Size

(for Clastic)*

Grain Rounding and

Sorting (for Clastic)*

Grain composition

(for Clastic)*

Cement (clastic) or

Mineral (chem) Composition

Acid

Test

Fossils Name

H

I

J

K

L

M

N

O

Name:_______________________________________________________ Date:______


61

Lesson Seven: Metamorphic Rocks Background Reading: Metamorphic Rocks

Metamorphic Rocks – These are rocks that have been changed from pre-existing

rock due to heat and or pressure, without melting.

Parent Rock (or protolith): These are both names for the rock that existed prior to

metamorphism. For example, limestone is a protolith that changes to marble due to

metamorphism. The igneous rock peridotite is a protolith that changes to serpentinite

(the California State rock!).

Grade: The grade of a metamorphic rock refers to the degree of change during

metamorphism and ultimately to the conditions present during metamorphism. We will

consider three general categories of grade: low, medium, and high grade. Low grade

rocks have been subjected to low degrees of heat and/or pressure, whereas high grade

rocks have been subjected to high degrees of heat and pressure.

Metamorphic Process include heat, pressure and fluid migration through the rock. All

three of these can cause ions (atoms that are in the pre-existing rock) to migrate to new

locations where they form new minerals. One of the changes we will see is the presence

of new (often shiny or sparkling) minerals. Micas are often formed during

metamorphism and these can give the rocks a shine or sparkle depending on the size of

the mica crystals.

Something to keep in mind – minerals that were stable (were not changing) in the

pre-existing rock become unstable under the new heat and pressure conditions.

Therefore the atoms (ions) in the pre-existing minerals leave the mineral structure and

migrate to new positions to form new minerals. This is how the rock changes. These

changes can be very obvious when conditions allow for big, new, sparkly minerals to

be formed, or they can be subtle when the mineral changes only produce minor

changes in the texture or hardness of the rock.

Heat: this is the energy that drives ion migration and recrystallization. The new

crystals are stable at higher temperatures. Example: clays will often recrystallize to

form muscovite and biotite (micas).

Pressure: this causes compaction and the differential stress (more pressure in one

direction than another) can cause squeezing in a preferred direction. This occurs in

tectonically active areas. In these cases the minerals grow perpendicular to stress

direction and cause a texture known as foliation (see changes listed below).

Fluids – hot fluids facilitate migration of ions. Water in pore space of sedimentary

rocks provides often provide the fluids involved in this process.

Metamorphic Changes: We will consider the following types of changes that occur

during metamorphism: Texture changes and Mineralogical changes (changes in the

mineral composition of the pre-existing rocks.

62

Changes in Texture

Foliation – a preferred orientation of minerals is developed due to differential stress

(see pressure discussion). Foliation includes Slaty Cleavage, Schistocity, Gneissic

Banding. We will see example of these in the lab. In general you can think of

foliation as a “grain” or “fabric” in the same way that wood or cloth has a preferred

orientation that makes it easier to split or tear in a particular direction.

Crystalline Texture (non foliated) – quartz and calcite are equal-dimensional

crystals, so they do not align in a preferred direction to produce foliation. Instead the

crystals just tend to get larger with higher grades of metamorphism.

Porphyroblastic – Some minerals tend to grow more rapidly in the metamorphic

environment than others. Consequently large crystals can be formed within a smaller

crystalline rock. Garnets are good examples of crystals that form large crystals and

give a metamorphic rock a porphyroblastic texture (this texture is similar to the

porphyritic texstures of igneous rocks).

Mineral Changes in Metamorphic Rocks

During metamorphism, new minerals form which are stable in the new metamorphic

environment. Some minerals are good indicators of a specific grade of

metamorphism. These are called index minerals.

Index Minerals include chlorite (low grade), muscovite and biotite (med. grade),

garnet (med. to high grade)

Quartz, Calcite, Feldspars are stable in a variety of temperatures and pressures;

consequently, they are not good index minerals.

The new metamorphic minerals that are produced reflect the protolith (or parent rock)

Chlorite – forms from the ferromagnessium minerals in basalt

Micas – form from clays that are in sedimentary protoliths

Talc– forms from mafic minerals that are in ultramafic rocks such as peridotite

Serpentine –forms from the metamorphism of peridotite in the presence of water.

Metamorphic Environments: A metamorphic environment is the geologic/tectonic

settings where a metamorphic rock is formed. There are several ways of categorizing

these environments. The categorization presented below is similar to the one presented in

the textbook. However, I have lumped the environments under two big subdivisions:

Localized, and Larger Areas.

Localized (although some of these can occur over large areas)

Contact / Thermal: this environment exists when the intense heat of magma

“bakes” the surrounding rock. Contact metamorphic rocks are typically not foliated.

Batholiths can produce contact metamorphic zones that are several km wide.

Hydrothermal: this occurs due to the hot fluids associated with geothermal activity.

These rocks are typically not foliated and they may be associated with

contact/thermal metamorphic environments. The presence of water can cause more

intense ion migration and development of unique minerals. This environment is

common at mid ocean ridges (divergent boundaries). It may result in concentrations

of metals, such as those seen at “black smokers” under the ocean.

Fault Zones: this environment is produced from the pressure (low heat) associated

with faulting. Rocks formed in this environment develop a foliation that is usually

parallel to the fault plane. This is sometimes called Dynamic Metamorphism

Name:_______________________________________________________ Date:______


63

Larger Areas – these categories include environments that are not related to specific

sources of heat or pressure, but rather to a larger geologic or tectonic setting.

Burial Metamorphism – rocks formed in this environment are usually not foliated.

This environment results from the confining pressure generated at 8 or more km

deep; however, the stress is not differential so foliation is not produced. These are

usually low grade metamorphic rocks with only subtle changes.

Dynamothermal or Regional Metamorphism – This environment is associated

with mountain building and the tectonic activity of a convergent plate boundary

(subduction zone). This environment is capable of producing both differential stress

and heat present. Consequently the rocks are usually foliated. The variation of heat

and pressure within these environments can produce a variety of metamorphic

grades. This results in metamorphic that range from slates to schists to gneiss.

Most of our lab rocks are examples of rocks formed in a Dynamothermal

environment.

Subduction zones are unique environments where high pressures but relatively low

temperatures exist. When basaltic ocean crust (what is being subducted) is subjected

to these conditions (high pressure, low heat) it results in something called blueschist

metamorphism. The name comes from a bluish colored amphibole that develops

when the mafic rock (basalt) changes in this high pressure/low temperature

dynamothermal environment.

64

Metamorphic Rocks

Metamorphic Terms: Protolith (or precursor or parent rock): the preexisting rock (prior to metamorphism).

Grade: The degree of metamorphism; the amount of heat and pressure required to produce

the rock. Foliation: parallel planar orientation of minerals.

Textures: Textures developed during metamorphism can be used to determine the grade (degree)

of metamorphism and, in some cases, the protolith

There are two main types of textures: foliated and nonfoliated.

Foliated Textures:

Slaty Cleavage: near perfect, planar foliation of very fine-grained minerals

Phyllitic Texture: a “sheen” due to alignment of fine-grained (too small to see) platy

minerals Schistosity: new metamorphic minerals are visible. They often create a “sparkly”

appearance. Gneissic Texture: alternating layers of parallel to subparallel foliation of medium- to coarse-

grained platy minerals.

Nonfoliated Textures:

crystalline: mass of crystals Some Low-grade metamorphism of basalt, conglomerate, sandstone, or other coarse-

grained/crystalline rocks.

Minerals (these are in addition to minerals we have already studied in previous labs):

Chlorite: green platy mineral (think of this as a green mica) Garnets: red-brown, spherical (polyhedral), glassy mineral

Serpentine: mineral group that includes greenish white minerals (actinolite, lizardite)

Metamorphic Rocks:

Foliated Metamorphic Rocks (distinguished by grade and foliation):

Slate,

Phyllite,

Schist,

Gneiss

Nonfoliated Rocks (distinguished by the minerals present):

Quartzite,

Marble,

Greenstone (low grade basalt)

Foliated or nonfoliated:

Serpentinite (low-med. grade)

Metaconglomerate (low-med grade)

Name:_______________________________________________________ Date:______


65

Typical transition in mineralogy during progressive metamorphism of shale

Increasing Metamorphism

Low Grade Intermediate Grade High Grade

Mineral Composition

Chlorite

Muscovite (mica)

Biotite (mica)

Garnet

Quartz

Calcite

Metamorphic Rock Type

Shale - Slate - Phyllite Schist Gneiss (no alteration)

Metamorphic Rock Classification

Foliated Metamorphic Rocks Non-Foliated Metamorphic Rocks Sometimes foliated

Name Grade Protolith



Slate Low Shale

Phyllite Low/Med Shale

Schist Med –High Variable

Gneiss High Variable

Quartzite Variable Quartz-rich Sandstone, Chert

Marble Variable Limestone

Greenstone Low grade Basalt

Serpentinite Low Peridotite

Metaconglomerate Low/Med Conglomerate

66

Worksheet 7.1: Metamorphic Rocks

1. The diagram above provides an example of how metamorphic foliation develops. To

help clarify the difference between sedimentary bedding and metamorphic foliation,

use this example to fill out the table below with the orientation of each structure in

each step of the diagram above. The orientation can be horizontal, vertical, angled

or not present (if the structure does not exist at that step).

Orientation of

structure:

Step 1 Step 2 Step 3

Sedimentary

Bedding

Metamorphic

Foliation

2. Use the following vocabulary to fill in the blanks in the paragraph.

Atoms

Minerals

Rocks

In most cases (except where rocks are highly altered by hydrothermal fluids), _________

do not significantly change overall chemical composition during metamorphism, so

the __________ in the metamorphic rock will essentailly be the same as the ___________ in

the protolith. However, the _____________ can combine in new ways under heat and

pressure creating new ____________ that were not present in the protolith.

Name:_______________________________________________________ Date:______


67

3. Use the letter L, I, H to show which of the following minerals indicates a Low,

Intermediate, or High grade metamorphic rock. Write “All” if the mineral does not

provide evidence of a specific grade. Refer to the information on page 65.

a. garnets ______ b. chlorite ________

c. quartz _______ d. muscovite and biotite_____

The diagram below shows the theoretical pressure-temperature space of the crust. The

lines with arrows represent possible paths that a metamorphic rock might take though the

pressure and temperature space. The letters A-D represent points along those paths.

4. Match each of the letters A-D in the diagram above with the number in the cross

section below that corresponds to the location where the pressure temperature

conditions would occur.

68

5. Label each of the lines with arrows on the pressure-temperature diagram on page 67

with one of the following descriptions:

Mountain Belt Metamorphism

Contact Metamorphism

Subduction Metamorphism

6. Read each of the following rock descriptions. After each rock description write the

letter corresponding to the zone in the pressure-temperature diagram where the rock

would most likely form.

________ Blueschist: This rock gets its name from the mineral Gluacaphane, a

bluish colored amphibole that is stable at high pressure and low

temperature.

________ Gneiss: High grade, foliated metamorphic rock. Minerals separate into

bands of minerals with similar chemistry.

________ Hornfels: A non-foliated metamorphic rock that varies in mineral

composition, but is often quite hard and may contain high-grade

metamorphic minerals.

________ Phyllite: A low grade metamorphic rock that often contains graphite,

chlorite and muscovite. It has a shimmery appearance.

Name:_______________________________________________________ Date:______


69

Lab 7.2: Metamorphic Minerals and Known Metamorphic Rocks

Minerals: Use the samples provided to answer these questions

Describe how to distinguish chlorite from mica (muscovite and biotite)

Describe three properties that help one distinguish quartz from calcite.

Describe the rock sample made of the serpentine group of minerals

Describe amphibole

Describe garnet

Known Metamorphic Rocks, use the labeled specimens to determine:

Rock Set 1:

How can you distinguish Quartzite from Marble?

Rock Set 2:

How can you distinguish Slate from Phyllite?

How can you distinguish Phyllite from Schist?

How can you distinguish Schist from Gneiss?

Rock Set 3:

How can you distinguish Chlorite Schist from Serpentinite?

How can you distinguish Greenstone from Serpentinite?

Rock Set 4:

How can you distinguish Gneiss from Quartzite?

Rock Set 5:

How could you tell a metaconglomerate from a conglomerate (sedimentary rock)?

70

Lab 7.3: Unknown Metamorphic Rocks:

Provide the metamorphic textures, minerals, grade, protolith and the rock name for each of these specimens. Only list the minerals

you observed. * Grade and Protolith may be indeterminate for some rock types. Write NA in these sections if grade or protolith

cannot be determined.

Specimen Foliated or Non-

foliated?

Minerals

(if visible)

Acid Test

(if it applies)

Metamorphic

Rock Name

Grade*

(if it applies)

Protolith*

(if it applies)

A

B

C

D

E

F

G

Name:_______________________________________________________ Date:______


71

Specimen Foliated or Non-

foliated?

(For foliated, list the

type of foliation)

Minerals

(if visible)

Acid Test

(if it applies)

Metamorphic

Rock Name

Grade*

(if it applies)

Protolith*

(if it applies)

H

I

J

K

L

M

N

72

Sedimentary and Metamorphic Rock Lab Quiz - Study Guide

You may use a sheet of notes (two sides of 8.5x11 inch paper). Computer generated

text is OK, but no photocopies are allowed. You will not be able to use your labs. You

may, however, transfer lab information to your sheet of notes.

Sedimentary Rocks – Be able to identify and describe the properties of:

Clastic Sedimentary Rocks:

Conglomerate,

Breccia,

Quartz-Rich Sandstone (Arenite),

Feldspar-Rich Sandstone (Arkose),

Mud-Rich Sandstone (Graywacke),

Mudstone (Shale),

Chemical/Biochemical Sedimentary Rocks

Fossiliferous Limestone,

Crystalline Limestone,

Micrite

Chert

Diatomite

Chalk

Sample Sedimenatary Rock Questions

List the sedimentary rock name

What is a distinguishing characteristic in this rock?

List the name of the mineral that makes up most of this rock

List a distinguishing characteristic of this rock

What mineral is common in this rock

Explain your criteria for assigning this rock name.

Photos of Sedimentary and Metamorphic Rock Specimens can be found on the

course Canvas web site. They are also at the following URLs:

Sedimentary Rock Photos:

http://tinyurl.com/g1sedrocks

Metamorphic Rock Photos:

http://tinyurl.com/g1metrocks

http://tinyurl.com/g1sedrocks

http://tinyurl.com/g1metrocks

Name:_______________________________________________________ Date:______


73

Metamorphic Rocks– Study Guide

Terminology:

Protolith, Grade, and Foliation. Be able to list these (if appropriate ) for a given sample.

Minerals

Be able to identify distinguishing minerals: quartz, calcite, muscovite, biotite, chloritie,

amphibole, garnet

Know the characteristics and rock names of the following rock types:

Foliated Metamorphic Rocks:

Slate

Phyllite

Schist

Gneiss

Non-foliated Metamorphic Rocks

Marble

Quartzite

Greenstone

Foliated and non-foliated varities

Serpentinite.

Metaconglomerate

Sample Questions for Metamorphic Rocks:

List the protolith for this rock.

List the name of this metamorphic rock

List the metamorphic grade

List one of the metamorphic minerals present in this rock (other than quartz)

List the metamorphic texture of this sample

Identify the rock sample using the specific rock name (this may be a igneous,

sedimentary, or metamorphic rock).

There will be one or two samples that can be any rock type (igneous, sedimentary,

metamorphic)

Name:_______________________________________________________ Date:______


75

Lesson Eight: Structural Geology Background Reading: Structural Geology

Deformation of Rocks (Structural Geology)–

Rocks are deformed in a variety of ways, but ultimately the deforming (bending or

breaking) is the result of the rock being under stress.

Stress is defined as a force applied over a given area. Push your hand down on a table.

You are applying a force to the area beneath your hand and as a result, stress has

developed.

The motion of plates and the overlying weight of rocks cause rocks to be stressed.

There are three principle types of stress:

Compression: material is squeezed (pushed together)

Tension: material is pulled apart (stretched)

Shear: material is torn (moves side-by-side)

For our discussion, the material in all of these situations is rock.

Strain is the change in shape that results from stress.

Stress causes deformation (bending and breaking) that results in strain (a change in

shape). In other words, stress causes strain.

There are two principle types of deformation – brittle deformation and ductile formation.

Brittle deformation occurs when a material breaks. A rock breaking during faulting is an

example of brittle deformation.

Ductile deformation occurs when a material bends (and does not snap back). A rock

bending during folding is an example of ductile deformation.

In this lesson we will be discussing two main categories of deformation – the folding of

rocks and the faulting of rocks. Either of the two can occur when rocks are under the

stresses that result from plate motions.

What determines if a rock folds or faults? The main factors are:

Temperature, Pressure, Time (deformation rate), and Composition (what the rock is made

of).

In general, rock that is at higher temperatures and pressures, and stressed over a longer

time period will experience folding (ductile deformation) and rock that is at lower

temperatures and pressures and stressed more quickly will break. For this reason,

geologists find that rocks behave in a ductile manner (and fold or flow) when they are

buried at depths greater than 10km to 15km. Rocks closer to the surface are more likely

to fracture or fault (behave in a brittle manner). However, rocks may experience both

folding and faulting within the same rock and at a similar depth. Sometimes as rocks

fold, they are brittle enough to eventually break and produce a fault. Humboldt Hill

(behind CR) is an example of a hill produced by both folding and faulting (the Little

Salmon Fault that dips under the campus).

76

Folding

Folded Rock can be described in terms of either arched up folds (called anticlines,

see the figure below) and arched down folds (called synclines). Each fold consists

of two limbs of the arch and a hinge line at the top (or bottom of the trough) that is

called the axis of the fold.

Anticline has the oldest strata in the center (near axis) and dips away from the center (axis)

Syncline has the youngest strata in the center and dips inward toward the center (the axis) ]

An example of an anticline and syncline occurring together is shown

below: Drawing by Bazard, 2012

Name:_______________________________________________________ Date:______


77

Orientation of strata that has been tilted as part of a fold.

When only one limb of a fold is exposed, it appears as a tilted block of strata. The

orientation of titled strata is described by two properties called Strike and Dip.

Strike and Dip provide the orientation of the strata with respect to north, east, west,

and south.

Strike and Dip:

•Dip: Angle between horizontal and the bedding surface (plane surface). •Down-Dip Direction: direction of the bed dip.

•Strike: Line perpendicular (90°) to down-dip direction. Line formed by intersection of

horizontal plane and strata plane

Two examples showing the Strike and Dip of strata (part of a fold limb):

Map symbol showing Strike and Dip: Strike Line is parallel to the contact between types of strata. The

Dip Direction is always 90 to the Strike Direction

The geologic map shows strikeand dip symbols. The dip angle is shown in the cross-section.

Strike and Dip

Map Symbol:

78

Faulting (brittle deformation): A fault occurs where stress causes a rock to break

and produces motion between opposite sides of a fracture. Faults are surfaces (like a

sheet of paper or plywood) that are called fault planes. The orientation of the fault

plane can also be described in terms of strike and dip.

I Dip-Slip Faults - These types of faults result in motion of rock up and down the dip of

a fault plane.

USGS public domain figure Normal Fault: This is caused by horizontal Tension . Normal faults result in lengthening

as the overhanging block (hanging wall) of a fault moves downward.

USGS public domain figure Reverse Fault (or “thrust” fault): This is caused by horizontal Compression,

Reverse faults result in shortening as the overhanging block (hanging wall) of a fault

moves upward. Thrust fault shallowly dipping (<45 degree) reverse fault.

USGS public domain figure

Strike-Slip Faults: Faults motion is parallel to the strike of a fault

Right-Lateral: Objects across fault move right

Left-Lateral: Objects across fault move lef

Name:_______________________________________________________ Date:______


79

Worksheet 8.1: Moonstone Beach Field Trip Preparation

All Figures by Emily Wright 2017

One of the goals of the Moonstone Beach field trip is to practice using a compass and

working with maps. To prepare for this, we will do some practice on campus first. The

compasses that we will use are Brunton Pocket Transit compasses. The class set includes

two different forms of notation. Azimuth (360°) and Quandrant notation.

1. Fill in the numbers that belong in the empty boxes in the diagram above, by observing

the pattern shown in other quadrants.

2. Write out the bearing of each of the gray lines in the illustration below. Use the

example provided to guide you in how to write out quadrant notation.

80

3. On the map provided below, use a protractor (provided in class) to draw the following

bearings:

a. A bearing of 340° from point A

b. A bearing of N80E from point B

4. On the diagram at right, observe

the layout of the azimuth

notation and the cardinal

directions. What is unusual

about the layout of the

directions?

Name:_______________________________________________________ Date:______


81

5. Use the compass illustrations below to answer the following questions?

a. In what direction is the sighting arm pointing on Compass 1? (Use

azimuth notation for your answer)

b. In what direction is the sighting arm pointing on Compass 2? (Use

quadrant notation for your answer)

6. Brunton Pocket Transits are commonly used by geologists in part because they

also include an inclinometer. In the sketch below, what is the dip (angle from

horizontal) of the rock?

82

We will now construct a practice map of some flags put out in the lawn. You will need a

compass (depending on class size, you may need to work in pairs) to take bearings and

you will use your pace to measure distance.

Your pace is the length of two steps. Choose your favorite foot (left or right) and count

the number of times that foot lands.

Landmark Type Bearing

back to

last

Beaing to

next

Paces to

next

Meters to

next

Millimeters

to next (for

map)

7. Fill out the first five columns of the data table above with the data you gather in

the “field”.

8. How many paces did it take you to walk 30m? (This number will be unique to

you)

9. Use this information to find your personal pace length in meters.

10. Fill in the column “Meters to next” using your pace length as a conversion rate.

11. As a class, we will decide on an appropriate map scale. Write down the scale

here:

12. Use the map scale to fill out the last column of the data table above.

We will construct our map as a class. You don’t need to draw anything at this point, but

pay attention to the methods, as you will need to perform these on your own with data

from Moonstone Beach.

Name:_______________________________________________________ Date:______


83

Worksheet 8.2: Geologic Structures

1. Write out the strike and dip measurement that is shown by the symbol below. Use a protractor to

determine the strike. Write the strike in Quadrant format. You may want to refer to pg. 77

Strike:________________ Dip:_______________Dip Direction:__________

2. Convert the strike from the previous question into azimuth.

3. Draw the symbol for the following strike and dip measurement: 015°, 45° SE

4. Consider the following blocks (a, b, c) and answer the following for each

a. describe the stress for each (tension, compression, shear)

b. use half arrows to show the sense of motion on the fault

c. for “a” and “b”, how will the dimension “l” change (shorter or longer)

d. label each type of fault

84

5. For each of the fault cross sections below, label the Hanging Wall (HW), the Footwall (FW), draw

the appropriate half-arrows on the fault and provide the fault name (there may be repeats).

6. Write a general rule for the age of geologic units in synclines and anticlines:

Syncline:

Anticline:

7. Write a general rule for the dip of the limbs of a syncline and anticline:

Syncline:

Anticline:

8. On the map at right draw in the

following. It may help to consult pg.

76 and 77.

a. The axis of the fold with the

appropriate symbol for the type

of fold and the plunge direction

(if applicable)

b. Strike and dip symbols on either

side of the fold axis with dip

measurements included (use a

protractor and the cross section)

Name:_______________________________________________________ Date:______


85

Lab 8.3: Geologic Maps Figures in this lab were modified from the public domain USGS Geologic Map Series

Part A: Masonville Quadrangle

This activity is designed to accompany the Geologic Map of the Masonville Quadrangle,

available in full size and color in class.

1. To get a sense of the overall patterns in the geology, on the small version of the map

on pg. 89, color in the following three units. Text and symbols on the small map are

too small to read, so look for large scale trends. Also write the symbol for each unit

(example: Ksf), the rock type(s) and the age (example: Cretaceous)

Dakota Group (Use one green for all the different formations in the Dakota Group)

Symbol:

Rock Type:

Age:

Lyons Formation (light blue)

Symbol:

Rock Type:

Age:

Fountain Formation (purple)

Symbol:

Rock Type:

Age:

2. There is a lot of yellow on the map that doesn’t follow the same pattern as the other

colors, what is this and why does it not follow the pattern?

3. Locate the Devil’s backbone. (It is just north of the Big Thompson River in the

eastern part of the map). A rock attitude measurement (strike and dip) has been taken

at a road cut in the Morrison Formation (Jm) on Highway 34. Locate the appropriate

symbol on the map. Use a protractor to measure the strike, then write out the

measurement in the form: strike, dip, dip direction

86

4. In the following two questions, you will use the map and the B to B’ cross section to

determine the attitude (strike and dip) of the Niobrara Formation on the east side of

the map. This will be an estimate rather than a precise measurement. The attitudes

plotted on the map are actually precise measurements made with a compass in the

field.

a. Observe all the strike and dip symbols along the Devil’s Backbone. Notice that the

strike lines are generally parallel to the green color stripe on the map. Use this same

concept to estimate the strike of the Niobrara Formation (Kns) on the eastern edge of

the map, right near the B’ end of the cross section line. Write your answer in the

appropriate space below the next question. (Refer to Worksheet 8.1 Question 8 on

page 84)

b. Using the B to B’ cross section, measure the dip of the Niobrara formation (Kns) unit

near the B’ end of the cross section. You will need a protractor.

Strike (part a):__________Dip(part b): _______Dip direction(part b): _________

5. Using the information from the previous question, draw the appropriate symbol for

the strike and dip on the copied map section below. Try to make your symbol

roughly the same size as the symbols already on the map.

Name:_______________________________________________________ Date:______


87

6. Locate the Big Thompson Anticline on the map. Is the Big Thompson Anticline

plunging or nonplunging? If it is plunging, in which direction does it plunge (as in

North, South, East or West)?

7. Draw a sketch below of the symbol used along the line that marks the axis for the Big

Thompson Anticline. Label the part of the symbol that indicates an anticline as well

as the part that indicates direction of plunge.

8. If there were no symbol on the map, what information would you use to determine the

direction of plunge?

9. True or false: the geologic unit in center of the Big Thompson Anticline is the oldest

unit.

10. True or false: the limbs of the Big Thompson Anticline dip toward the axis.

11. Locate a syncline on the map. Circle the syncline on your small map.

12. On the small map, I have added a C to C’ line. Complete the cross section that has

been started for you below. Color in the units using approximately the same colors as

the map. Add dotted lines to project the units above ground (where they would have

been before they were eroded).

88

13. Locate the Green Ridge Fault on the map and in the B to B’ cross section. Use a red

colored pencil to trace over the line on your small map.

14. Below is a blow up of the Green Ridge Fault in cross section. Use the Fountain

Formation (PPf) to determine which way the fault has been offset. Add half arrows to

the blow up below. What type of fault it this (Normal, Reverse or Strike-Slip)?

Part B: Geologic Map of the Eel River Basin

Use the Geologic Map of the Eel River Basin (provided in class) to answer the following

questions:

15. Locate the CR campus. What are the brown Quaternary deposits in the hills above

campus?

16. What geologic structures are present in the map area? How have these structures

shaped the topography (hills and valleys ect.)?

17. Find the natural gas wells on Tompkins Hill. Are these wells located on a syncline or

an anticline?

Name:_______________________________________________________ Date:______


89

Name:_______________________________________________________ Date:______


91

Lesson Nine: Geologic Time Background Reading: Geologic Time

Relative age dates are determined by placing rocks and events in their proper sequence

of formation

General Principles of relative age dating:

1. Superposition

In an undeformed sequence of sedimentary rocks (or layered igneous rocks), the

oldest rocks are on the bottom.

2. Principle of original horizontality

Layers of sediment are generally deposited in a horizontal position.

Rock layers that are flat have not been disturbed.

3. Principle of cross-cutting relationships

Younger features cut across older features. So faults cutting through rocks are

younger than what they cut through. Igneous intrusions that cut through rocks are

younger than the rocks they cut through. Also, an erosional surface that cuts across a

body of rock is younger than the underlying body of rock.

5. Fossil Succession

6. Unconformity

An unconformity is a break in the rock record produced by erosion and/or

nondeposition of rock units.

7. Inclusions

An inclusion is a piece of rock that is enclosed within another rock.

Rock containing the inclusion is younger than the inclusion.

Numeric Time: Numerical dates –the actual number of years that have passed since an

event occurred (also known as absolute age dating).

Numeric time methods use a process that happens at a known rate.

Modern numeric dating in the geologic sciences is based on many types of known rates

such as tree ring dating where we know the rate of growth of rings (summer and winter

rings) or lichen growth on boulders (to determine how long the boulder of a landslide has

been sitting in one place).

However, most numerical ages come from analysis of radioactive decay of elements that

are within minerals or other compounds. This is called “Radiometric Dating” or

“Isotopic Dating”

Radiometric dating (or Isotopic dating) is based on the transformation of one element

into either another element or an Isotope of that element.

An Isotope is an element with the same number of protons (same element) in its nucleus

as other isotopes of the same element, but it has a different numbers of neutrons.

For example: Carbon-12 and Carbon 14 are both isotopes of the element carbon. Both

have six protons in their nucleus (this is what defines them as being carbon). However,

92

Carbon 12 has six neutrons and Carbon 14 has eight neutrons. Therefore Carbon 14 is

actually heavier than Carbon 12.

Transformation Process of Radioactive Decay

Parent material decays to a daughter product

Rate of Decay is the “clock” that allows determination of time. This is what happens at a

known rate to allow a numeric age to be calculated

Half-Life: the amount of time it takes for half of atoms in unstable parent material to

decay to a stable daughter product.

Each atom has 50% chance of decaying to the new material in 1 half-life Radioactive decay is an exponential decay: new decay is a percentage of remaining

material.

Assumptions of Radioactive Decay Analysis

• Minerals are closed systems, or loss and gain can be accounted for.

• Initial Parent and Daughter are known.

• Decay rate is constant for each element (isotope) and cannot be affected by pressure or

temperature.

This is a statistical method based on probability (50% chance of decay in one half life).

Statistics are only valid for large data sets. The atoms in a mineral represent a very

large data set.

Importance of radiometric dating

Radiometric dating is a complex procedure that requires precise measurement

Rocks from several localities have been dated at more than 3 billion years

This confirms the idea that geologic time is immense

Limitations:

Not all rocks can be dated using radiometric dates – requires unstable material.

It is important to know what is being dated. If the isotopes are from igneous or

metamorphic crystals, then the ages are the age of crystallization (from magma or

metamorphism). In the case of Carbon-14 isotopes, the dating provides the age

when the organic material stopped taking in carbon (the death of the organism)

The half life of an isotopes limits the age range that can be provided by the

isotopes. Carbon-14 isotopes decay relatively rapidly so it can only date materials

within the last 50,000-70,000 years. Uranium isotopes have very long half lifes

and can be used to age date material several billion years old.

All age dates include estimates of error. The error estimates are based on the

precision of lab equipment and our knowledge of parameters such as how well we

know the half lifes or the initial content of an isotope in the environment. It is

important to understand the error estimate before applying the age to a geologic

study.

Name:_______________________________________________________ Date:______


93

Mathematical Reasoning Behind Radioactive Decay Analysis. The following is provided for those who have an interest in the mathematics used to derive

radiometric ages. It will not be on the test

How do scientists determine the Half Life if it is thousands (or millions to billions of years) long?

Good question – here is a general description of the mathematics and reasoning used to determine

the half life for a particular element (or isotope):

Radioactive Decay is an exponential process. Therefore “it can be shown” that the following is

true: Natural logarithm (or ln) of Nt/No = kt This is equation #1: ln (Nt/No) = kt

Where: No = amount of parent at a beginning time

Nt = amount of parent after time t k = unique decay rate for the material, and is called the decay constant

After one half-life has elapsed: Nt/No = 1/2

So when t=one half life, equation #1 is: ln (1/2)= kt

Therefore The half-life= ln (1/2) / k This is equation #2

k (the decay constant) can be determined by analyzing the relationship shown in equation #1 for a short amount of time. If t is known and Nt and No can be measured (over a short time) then one

can solve for k,

Once k is known then one can solve equation #2 for the value of the half-life. This is how half-

lifes are determined – by using shorter amounts of time to determine k, and then using equation #2 to solve for the half life.

94

Worksheet 9.1: Relative Time

Refer to the geologic profile shown below. Note that W, L, M, O, A, P, and J represent

the time of deposition of sedimentary strata. B and K represent the age of igneous

intrusions. C represents the age of the fault motion.

1. List the letters shown to provide a plausible sequence of geologic events (from oldest

to youngest) to account for this profile.

2. The specific name for the contact represented by the letter U is: _________________.

Describe the sequence of events that formed U:

3. Has intrusion B been tilted? What is your evidence?

4. Has intrusion K been tilted? What is your evidence? What additional evidence would

be helpful to better answer this question?

Name:_______________________________________________________ Date:______


95

Worksheet 9.2 -Absolute Time

Radioactive decay. Radiometric dating uses radioactive elements that decay by emitting

nuclear particles. These radioactive elements are called the parent material. In the

decay process they are transformed into new elements called the daughter material. The

rate of decay (how fast it occurs) is described in terms of a half-life. A half-life is the

amount of time required for half of the parent atoms to decay to the daughter atoms.

For example, one type of Uranium (235) has a half-life of 713 million years. The

daughter product is Lead (207). This means that after 713 million years one gram of this

Uranium parent would change leaving ½ gram of Uranium and ½ gram of Lead.

1. Consider the decay of Carbon-14. It has a half-life of 5730 years.

a. Complete the graph below to show how 100% of the Carbon changes over several

half-lifes.

b. How much parent (in %) is left after 4 half-lifes?

c. How old is this material (after 4 half-lifes)

d. Material older than about 50,000 years cannot be dated using Carbon-14. What is

the reason for this?

96

The Figure below shows an area where two igneous intrusions (dikes) cut across several

sedimentary layers. The intrusions (Igneous Dike A and B) are composed of igneous

rock that contains a small amount of unstable parent material. This is radioactive

Element (isotope) X. The other figure below shows a decay curve for Element X.

2. Use the decay curve to determine the half-life of Element X

3. Use the percentage of X to date:

a. The age of metamorphism of the schist

b. The age of the intrusion of A (age of crystallization)

c. The age of the intrusion of B (age of crystallization)

4. What is the possible age range of layers 1-4?

5. What is the possible age range of layers 5-11?

6. What is the maximum age of layer 12? Figures: Bazard, 2012

Name:_______________________________________________________ Date:______


97

Worksheet 9.3: Geologic Time Scale

Geologic time has been subdivided into different units of time. This was done in the 19th

century based on relative time principles and the fossil record. Numeric ages were added

in the 20th

century. The subdivisions are based on major changes in life form (fossils)

and/or climate (as it influences life forms and rock types)

1. Write the following terms in order of size of the geologic time unit (largest to smallest): Period,

Eon, Epoch, Era.

2. Provide the numeric time for each of the following:

Holocene

Epoch:

Cenozoic Era:

Phanerozoic

Eon:

Quaternary

Period:

NP

S P

ubli

c D

om

ain

98

Lab 9.4: Geologic Map of California

1. Find a location where some of the oldest rock in California is found. There are

several locations with the oldest rock types.

a. List a geographic location near at least one of them.

b. What is the age and rock type?

2. Describe the geology of the Sutter Butte region. What is the age of the rock and how

do you think it was formed?

3. Look for linear trends and see if you can locate the San Andreas Fault on this map.

Cite evidence from the map that indicates that there has been relative motion across

this fault. Use the sense of motion to describe the type of fault that is present.

4. What is the age and rock type common in the Modoc Plateau region (northeastern

California)

5. Find Yosemite Valley. What is the type and age of the rock surrounding this valley?

What is the significance of the Qg unit?

Lesson Ten: Landscape Evolution Background Reading: Topographic Maps

Latitude: Angle from the Equator, with the equator being zero and the poles being 90

degrees (either North or South). (National atlast.Gov - Public Domain)

Longitude: Position around the globe. Looking down at the pole and considering the Earth

as a 360 degree circle. (National atlast.Gov - Public Domain)

Rules for contour lines

1. Every point on a contour line is at the same elevation.

2. Contour lines always separate points of higher and lower elevation. You must

determine the up and down direction by examining adjacent features (valley, hill)

3. Contour lines always close to form a loop.

4. The Contour Interval is the elevation distance between contour lines. Every fifth

line is heavier and is known as an index contour

5. Contour lines never cross one another, except in the very rare instance of an

overhanging cliff (in that case the hidden contour is dashed)

6. Evenly spaced contour lines indicate a uniform slope.

7. Closely spaced contour lines indicate a steep slope. Widely spaced contour lines

indicate a shallow slope.

8. A series of closed contours (irregular circle) indicates a hill. Depressions look

similar but have hachure marks on the inward side of the contour line.

9. Contour lines form a V pattern when crossing streams. The narrow part of the V

points upstream.

100

Background Reading: Landforms

Landforms are a result of Uplift/Subsidence combined with Erosion/Deposition.

Relative balance of uplift/subsidence and erosion/deposition determines the landscape.

Uplift and Subsidence occur from folding, faulting, earth’s heat, and accumulation at

volcanic centers.

Erosion is caused by gravity that results in the movement of rock, water, and ice. Erosion

also results from wind (solar energy) and chemical reactions.

Deposition results when these process slow and sediment stops being transported.

When erosion and deposition are dominant, the landscapes become flatter and valleys

broader.

When uplift and subsidence are dominant, landscapes have more relief and valleys are

deeper.

Relief is the elevation difference between two points.

Base Level – the level to which a stream erodes. Local base levels are the elevation of a

lake or valley. The “ultimate” base level is sea level. However, some base levels are

below sea level (can you guess where this would occur?).

Geomorphology Concepts of William Morris Davis – this is a historic starting point.

Most modern geomorphologists don’t agree with the simplicity of Davis’ cycle and his

concept that there is an “evolution “ of landscapes. However, his stages are still useful in

understanding the influences on landscapes.

Youthful Stage - active downcutting brought on by a base level change. This is caused

by tectonic uplift and/or sea level drop. This produces rugged, high-relief landform

Mature Stage – erosion and deposition begin to dominate and return the landscape to a

lower-relief form. Peaks become rounded and river profiles become more gradual.

Old Age – erosion and deposition dominate. Stream profiles become very gradual and

the land elevation begins to approach the elevation of base level.

More modern ideas incorporate ideas of thresholds being reached, feedback, climatic

changes and tectonic changes. These models can be quite complex.

Mass Movement refers to the downslope movement of rock, regolith, and soil under the

direct influence of gravity. •Geologic process that often follows weathering

•Combined effects: mass wasting and running water produce slopes and stream valleys

•Mass Movement results in landform development

Colluvium (a definition): loose unconsolidated deposit at the foot of slopes (landslide deposits)

•Driving Forces: related to weight of materials (gravity acting on mass is weight). This

includes weight of rock, weight of vegetation, weight of water, weight of human

endeavors (houses, roads, underground tanks, pools, etc.)

Resisting Forces: related to the shear strength of materials. This includes the strength of

rocks, roots, the down-slope portion of a slope, and manmade structures such as walls,

tie-backs, etc. The following contribute to the resisting force: - Gravity pushing down on surface is a resisting force

- Strength of earth material (Shear Strength)

- Cementationand friction between grains

- Orientation of bedding (stratification) and orientation of foliation or rock fabric

- Vegetation (increasing shear strength)

- Buttressing of Slope (Toe of Slope)

Important Factors for Mass Wasting

•Steepness of Slope: Greater component of gravity –Percent Grade= (Rise/Run)*100 = (elev change/ horizontal)*100

•Water:

–Small amounts of water increases cohesion and adds strength

–Usually water adds weight (driving force) and reduces shear strength

•Vegetation –Adds to shear strength (roots)

–Removes water (transpiration)

–Provides Protection from direct impact of rain

–Adds weight, which may be a driving force

•Rock Type

–Wet clays and poorly cemented rock= low shear strength

–Strike and Dip: orientation of bedding

–Foliation: orientation of planar elements

What determines these factors?•Steepness of Slope: –Tectonic Forces (uplift); Earth Materials

–Slope Modification: nature (rivers), people

•Water:

–Climate

–Drainage

–Vegetation

•Rock Type

–Nature

–Modification by Humans

Classification:

Flows • Debris Flow / Mudflow (including a lahar)

• Earth Flow (on slopes, rather than drainages)

• Creep

Slides

Rotational (slump)

Translational (rock slide)

Falls

Rock Fall and debris falls

Subsidence

Slow – Basin collapse

Rapid – Sink holes

102

River Systems I Terminology:

Discharge: the volume of water passing a point per time

Load: volume of sediment being transported by a river

Drainage Basin (watershed)/Drainage Divide: Entire area drained by a river system;

separated from other drainage basins by a drainage divide

Headwaters/Mouth (delta): beginning and end of a stream; steep to flat gradient.

Rivers flow from the headwaters to the mouth (location of a delta). This system includes

tributaries that flow into the trunk stream that eventually flows to a mouth.

Tributaries: smaller streams that feed into a central channel (or trunk).

Channel, Bed, and Banks: area where water flows (other than at times of a flood).

Floodplain: flat, low-lying area flanking a stream that is subjected to flooding.

Gradient: relief compared to horizontal distance.

Profile: change in gradient along the course of a river. A river profile is typically steep

near the headwaters and flatter near the mouth.

Changes in uplift, rate of erosion, discharge, and base level effect the stream profile.

II Concepts and Processes:

Base level: a level below which a stream cannot erode its valley; ultimate base level is

sea level. Changes in relative base level influence the ability of a stream to erode and

transport sediment. Thus, base level changes influence stream profiles. These changes

involve relative down drop of base level, which can occur by uplift or base level drop

(sea/lake level drop).

Erosion and Deposition

Downcutting: vertical erosion. This process is enhanced by relative base level drop.

Headward erosion: Rivers erode upstream toward the headwaters. This erosion results

in the profile being adjusted to the base level. Meandering: side-to-side erosion. This process happens in a predictable way: deposition

on inside bends (or meanders) to form point bars; erosion on outside bends (or meanders)

to form cutbanks. When the gradient decreases, streams tend to meander.

Braided Streams: Excess sediment causes a stream to deposit sediment and then to

erode multiple channels through the deposit. This also occurs when a sudden decrease in

gradient occurs. A similar process occurs at the delta.

Delta Formation: As the gradient decreases near base level, a stream will deposit

material. As the river erodes its way through this deposited sediment, it forms a delta

(triangle-shaped landform).

Floodplain Formation: during flooding, sediment is transported out of the channel into

the slow moving water of the surrounding region. This sediment is deposited and forms

the floodplain.

River Terrace Formation: Drops in base level causes formation of a new floodplain at

a lower elevation. The former floodplain is a river terrace.

Drainage patterns reflect relief and regional steepness (topography), rock resistance (to

weathering), climate, hydrology (drainage, size of the drainage basin, permeability of

rock), structural controls on the rock (orientation of faults, folds, and uplifts)

Worksheet 10.1 - Mass Movement

Photo by permission of JimFalls - CGS

1. Evaluate the situation above (at Big Lagoon, CA) in terms of driving forces and

resisting forces. A beach adjacent to the Pacific ocean is at the base of the cliff. The

bluff is composed of young sandstone and mudstone layers. This picture was taken

shortly after a period of storms and high waves.

Resisting Forces (including how these forces were reduced):

Driving Forces (including what may have caused the slide):

2. Label each type of mass wasting using the classification described in the

textbook and on page 101.

a. The type of mass movement that takes place the most gradually

b. Mass movement involving a slurry of large clasts, and rapid movement.

c. The type of mass movement where a whole segment of rock moves down a curved

surface

d. Free fall of material from a steep slope (dry material)

104

Worksheet 10.2 - Rivers

1. Use the Letter “C” or the letters “PB” to show where at least two cutbanks and

point bars are located in the figure below.

Drawing: Bazard, 2013

2. The area between the arrows represents the:______________________________

3. Assume this river empties into a lake approximately one mile downstream. Describe

how the channel will change if the lake level drops by several hundred feet.

4. The arrows in the diagram above are pointing toward: ____________________

5. These represent former: _____________________________________

River

Worksheet 10.3 Landscapes

1. Provide a definition and example of the following:

Relief:

Agent of Erosion:

2. Provide the requested information for each of the following situations

A. A steep mountain range with a deep valley to the east. The valley is filled with a thick

accumulation of sediment. The mountain range is snow covered and prone to landslides.

The valley includes streams and a lake.

Is this situation dominated more by uplift/subsidence or erosion/deposition?

List the agents and processes of erosion at work in this situation

List the depositional processes at work in this situtation

B. A broad floodplain with little relief. A large river meanders across this floodplain

until it enters the ocean where a large delta has formed.

Is this situation dominated more by uplift/subsidence or erosion/deposition?

List the agents and processes of erosion at work in this situation

List the depositional processes at work in this situtation

106

Lab 10.4: Topographic Maps.

Goals: To become familiar with reading and interpreting topographic maps and using a

compass.

Concepts and Terms: Latitude, Longitude, Magnetic Declination, Public Land Survey

System, Principal Meridian, Base Line, Township, Range, Section, Scales, Contour

Lines, Contour Interval, Topographic Profile, Vertical Exaggeration.

1. Refer to the Quadrangle Map Provided

a. When was this map made?

b. What is the map scale?

c. What is the magnetic declination?

d. Provide the approximate latitude and longitude of the feature described by your

instructor

e. Draw a sketch showing how contour lines define a stream valley or creek bed.

2. Slopes (or grades) are often described in terms of percent. The percent is the vertical

change divided by the horizontal change times 100 (to be expressed as a percent):

A 25% slope is where the vertical change is 25% of the horizontal change. For example, you

move 100 meters horizontally and drop 25 meters: Note that the

percent of a slope is not the angle of the slope. In fact a 100% slope (which is so steep it is difficult to stand upon) is a 45° dip.

Determine relief, grade, and degree of slope at a specific location.

If time, additional activities related to topographic profiles may be added to this lab

verticalchange

horizontalchangeslope* %100 =

25

100100 25%

m

m* =

Lab 10.5 Maps of Landscapes

For this lab you will need a copy of Laboratory Manual in Physical Geology by Busch

and Tasa 5th or 6

th edition (Available for loan in class). Find the following maps within

and answer the questions below:

Map of Waldron Arkansas (pg. 189 6th

ed., pg. 181 5th

ed.)

1. Describe the overall topography.

2. Explain how the underlying geology determines the topography here. If you have

the 6th edition, consult pg. 175, 176 and 184. If you have the 5

th edition, consult

pg. 166 and 167.

Map of Ennis, Montana (pg. 192 6th

ed., pg. 184 5th

ed.) 3. Describe the overall topography.

4. What features can be attributed to tectonic uplift?

5. In what ways has erosion shaped this landscape? In what part of the map is most

of the erosion occurring?

6. In what ways has deposition shaped the landscape? What features are mostly

depositional?

7. What is or has been the major agent of erosion and deposition here (e.g. streams

and rivers, glaciers, ocean waves, etc.)? How can you tell?

108

Map of Glacier National Park (pg. 230 6th

ed.) or Map of Siffleur River, Alberta (pg.

213 5th

ed.)

8. Describe the overall topography.

9. What features can be attributed to tectonic uplift?

10. In general, is this landscape dominated by erosion or deposition?


and rivers, glaciers, ocean waves, etc.)? How can you tell (besides the name of

the park of course… consult the diagrams in Chapter 12 of the 5th ed. or Chapter

13 of the 6th ed.)?

Map of Ocean City, Maryland (pg. 256 6th

ed., pg.247 5th

ed.)


and rivers, glaciers, ocean waves, etc.)? How can you tell?

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