Rocks Lab 3 - Student Handout
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School
Colorado State University, Fort Collins *
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Course
121
Subject
Geology
Date
Dec 6, 2023
Type
docx
Pages
6
Uploaded by CoachHedgehogPerson992
GEOL 121
Tim Trostel
Lab Section L18
Rocks Lab 3 – Rocks of Colorado and Geologic Maps
Learning Objectives:
1.
Describe, Identify, and Interpret Rocks from Colorado
2.
Find information about the geology of a region from a geologic map
In this week’s lab, you will continue to practice your skills at describing and identifying rocks, this
time using rock samples from the Colorado Front Range. All of the rocks that you will see in lab
this week are rocks that you can see when you are out exploring around Fort Collins and in the
foothills. You will also use a geologic map to gain more detailed information about the rocks of
the Front Range.
Part 1: Rocks of the Colorado Front Range
For each unknown rock sample, you should provide:
1)
A detailed description. Your description should be detailed enough that someone
reading your description could easily pick out which rock you are talking about.
Your description should include information such as the rock’s color, texture, grain
size, minerals present, layering, fossils present, variability, abnormalities, etc.
2)
Whether the rock is igneous, sedimentary or metamorphic, and how you know.
3)
An identification of the rock.
4)
A hypothesis of how the rock formed and the evidence supporting your hypothesis.
Rubric for rock descriptions:
0.5 pt.
0.25 pt.
0 pt.
Descriptions contain enough detail that
someone reading the description could
picture the rock in their mind. Features
such as color, shape, texture, irregularities,
patterns, layering, grain size and shape,
minerals present, etc. are described when
appropriate.
Descriptions are given but
lack adequate detail to fully
under- stand what is being
seen.
No response given.
Rocks Lab 3
GEOL 121
Sample #
Rock Description
Rock Type (ign, sed, or
meta)
How do you know?
Rock ID
Formation Hypothesis
And Reasoning
Sample 1
Intermediate spotted with pink,
black, and white.
Igneous
The intermediate texture
Granite
Medium grained
Sample 2
Very smooth and flat with layers.
Dark gray color.
Sedimentary rock
Reacts to acid
Limestone shale
Reacts to acid
Sample 3
Pinkish red color with white
specks in it.
Sedimentary rock
Conglomerate, visible
smaller rocks inside of it.
Sandstone
Compacted with visible
rocks inside of it.
2
Rocks Lab 3
GEOL 121
Sample #
Rock Description
Rock Type (ign, sed, or
meta)
How do you know?
Rock ID
Formation Hypothesis
and Reasoning
Sample 4
Very shiny with a mix of dark
gray and salmon color. Flat
surface.
Metamorphic rock
Recrystallization of
mudstone with small
crystals.
Schist
Foliation
Sample 5
Lots of small black sheets of rock.
Sedimentary rock
Soft fine grain formed in a
calm energy area. Dusty
feel, brittle.
Shale
Soft fine grain formed in
a calm energy area.
Dusty feel, brittle.
3
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Rocks Lab 3
GEOL 121
Part 2: Geologic Maps
Take a few minutes and examine the map that has been provided.
1) What is this map showing you? What spatial area is this map showing? What do the colors
represent?
This is a geological map of Horsetooth Reservoir. The map is showing all the different
types of minerals in the area. The different colors represent the different types of minerals.
2) In what area of the map do you generally find igneous and metamorphic rocks? In what area
of the map do you generally find sedimentary rocks?
Igneous rocks are found near the water while metamorphic rocks can be found in the
areas with higher elevation. Sedimentary rocks are found in lower elevation areas near creeks.
3) Find the rock formation labeled Xbc on the map and in the legend.
What is the name, age, and
composition of the formation? Which of the rocks that you previously described best matches the
description for Xbc?
Boulder Creek Granodiorite, Proterozoic age, light to dark gray, medium
grained. The rock that matches best is sample 1.
4
Rocks Lab 3
GEOL 121
4) Find the rock formation labeled Xqs on the map and in the legend.
What is the name, age, and
composition of the formation? Which of the rocks that you previously described best matches the
description for Xqs?
Quartzofeldspathic gneiss, Proterozoic age, fine grained, and gray. The rock that matches
best is sample 4.
5) Find the rock formation labeled PPf on the map and in the legend.
What is the name, age, and
composition of the formation? Which of the rocks that you previously described best matches the
description for PPf?
Fountain formation, lower Permian, upper and middle Pennsylvanian age, reddish brown
and gray. The rock that matches best is sample 3.
6)
Find the rock formation labeled Kn/Kns on the map and in the legend.
What is the name, age,
and composition of the formation? Which of the rocks that you previously described best
matches the description for Kns?
Smoky hill shale member, upper Cretaceous age, dark gray on fresh surface. The rock
that fits best is sample 5.
7) Find the rock formation labeled Kpl on the map and in the legend.
What is the name, age, and
composition of the formation? Which of the rocks that you previously described best matches the
description for Kpl?
Pierre Shale, upper Cretaceous age, dark-olive gray shale and sandy shale.. The rock that
fits best is sample 5
8) Find Horsetooth Reservoir on the map.
a. Which formations form the east and west edges of Horsetooth Reservoir? What is their
composition?
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Rocks Lab 3
GEOL 121
The east contains the Morrrison formation from the Upper Jurassic age, green, red, yellow and
white claystone and siltstone. The west contains Lyons Sandstone from the Lower Premian age,
orange to pinkish gray, fine to medium grain, well sorted quartz sandstone.
b. Which formations are underneath Horsetooth Reservoir? What is their composition?
Lykins Formation, reddish-brown siltstone and fine grained sandstone.
9) Why do you think the reservoir was placed where it was?
It was formed on siltstone because it's waterproof.
10) What are one or two other potential ways that geologic maps such as this one could be used
by non-geologists to inform their decisions or planning?
Two other potential ways geologists can use this map for planning is knowing where it is safe to
build and what kind of mineral is below when drilling/digging.
6
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