Rocks Lab 2 - Student Handout
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Colorado State University, Fort Collins *
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Geology
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Dec 6, 2023
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GEOL 121
Name ________Jayse Wagner____________
Lab Section___01______
Rocks Lab 2 – Rock Classification and Identification
Learning Objectives:
1)
Describe the characteristics used to classify igneous, sedimentary, and metamorphic
rocks.
2)
Identify common igneous, sedimentary, and metamorphic rocks.
Part 1: Igneous Rocks
1) Igneous rocks form from the cooling and crystallization of magma. This cooling may happen
on Earth’s surface or deeper within the crust. Based on this understanding of how igneous rocks
form and what you learned in Rocks Lab 1, what characteristics of igneous rocks might be
useful for identifying and classifying igneous rocks?
The different materials found in the rocks, the texture of the rock, their reaction to acid, and
different mineral deposits.
2) Examine igneous rocks A, B, and C in your sample set:
What are some ways these rocks are similar?
What are some ways these rocks are different?
They are coarse in texture and have mineral
deposits.
The sizes and colors of the rocks differ.
3) Examine igneous rocks E, F, and G in your sample set:
What are some ways these rocks are similar?
What are some ways these rocks are different?
Rocks Lab 2
GEOL 121
They are all dark mafic rocks
The mineral deposits vary in size and the
composition varies.
Igneous rocks are classified according to their composition and texture. Composition
refers to the proportion of the different silicate minerals that are present in the rocks, and
can be simplified to the major catagories: felsic, intermediate, mafic, and ultra-mafic.
Igneous textures generally reflect the method and rate at which the magma cooled.
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4) For the unknown igneous rocks describe their composition and texture. Then use the
provided classification charts to identify the rock.
Sample
Composition
Texture
Rock ID
A
Felsic
Crystaline Phaneritic
Granite
B
Intermediate
Phaneritic
Diorite
C
Mafic
Phaneritic
Gabbro
D
Felsic
Aphanitic
Rhyolite
3
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Rocks Lab 2
GEOL 121
E
Intermediate
Porphyritic
Andesite
F
mafic
Aphanitic
Basalt
G
mafic
Vesicular
Basalt
5) How confident do you feel in your identifications?
Relatively confident
6) What is still unclear to you about igneous rock classification?
Grain Classifications
Part 2: Sedimentary Rocks
7) Sedimentary rocks form from the products of chemical and physical weathering. The
sediments and dissolved ions are transported and deposited by processes happening on
Earth’s surface. Based on this understanding of how sedimentary rocks form and what you
learned in Rocks Lab 1, what characteristics of sedimentary rocks might be useful for identifying
and classifying sedimentary rocks?
The grain size, hardness, and compostition
8) Examine sedimentary rocks K, O, and P:
What are some ways these rocks are similar?
What are some ways these rocks are different?
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Rocks Lab 2
GEOL 121
They all have small grain sizes and smooth
texture
Color varies, different deposit sizes
9) Examine sedimentary rocks J, L, and M:
What are some ways these rocks are similar?
What are some ways these rocks are different?
Not much is similar besides that they are rocks
Color, size of deposits
Sedimentary rocks are classified at the highest level according to the composition of the
material and the origins of the rock. Clastic/detrital rocks are the most common
sedimentary rocks; these rocks are further classified by their clast size.
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Rocks Lab 2
GEOL 121
10) For the unknown sedimentary rocks use the classification charts provided to identify the
rock and provide a justification.
6
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Rocks Lab 2
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Sample
Rock ID
Reasoning
J
Shale
Very small grain size and has plenty of different layers.
K
Quartz
Sandstone
Made mostly of medium sized quartz which are visible to the
naked eye
L
Sandstone
The grain pattern as well as some red coloring
M
Conglomerate
The rock deposits are rounded
N
Breccia
Rock deposits are angular
O
Fossiliferous
Limestone
It has micro grain sizes with visible fossils and light coloring
P
Bituminous
Coal
Black colored rock with soft layering
11) How confident do you feel in your identifications?
Pretty good not fully confident
12) What is still unclear to you about sedimentary rock classification?
How to determine rock grain sizes
Part 3: Metamorphic Rocks
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Rocks Lab 2
GEOL 121
13) Metamorphic rocks form through the alteration of other rocks by high heat and/or pressure.
This can happen during burial to greater depths, tectonic processes, or the movement of heat
by magma. Based on this understanding of how metamorphic rocks form and what you learned
in Rocks Lab 1, what characteristics of metamorphic rocks might be useful for identifying and
classifying metamorphic rocks?
The foliage and cleavage helps to identify these rocks
14) Examine metamorphic rocks R, W, and X:
What are some ways these rocks are similar?
What are some ways these rocks are different?
W and X are foliated but all of them are
somewhat coarse.
The colors and the size of their deposits
15) Examine metamorphic rocks T, U, and V:
What are some ways these rocks are similar?
What are some ways these rocks are different?
They have small grains and similar types of
cleavage
Their shape, color, and grain size
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Rocks Lab 2
GEOL 121
Metamorphic rocks are classified primarily based on their texture, most importantly the
presence and degree of foliation. Mineral composition and grain size also play a role in
classification.
9
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Rocks Lab 2
GEOL 121
16) For the unknown metamorphic rocks use the classification charts provided to identify the
rock and provide a justification.
Sample
Rock ID
Reasoning
R
Gneiss
Limited layering
S
Gneiss
Course grains
T
Mica Schist
Shiny-looking with a foliation formed
U
Phylite
Foliated with fine grains and cleavage is well devolped
V
Slate
There are no visible grains and its not foliated
W
Marble
a white color that fizzes with acid
X
quartzite
Fine-grained with no foliation
17) How confident do you feel in your identifications?
Most confident of the whole lab
18) What is still unclear to you about metamorphic rock classification?
Not much grain size Is still sometimes hard
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