Rocks Lab 2 - ALexi Lindsay
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Geology
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Dec 6, 2023
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GEOL 121
Name Alexi Lindsay
Lab Section____16_____
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?
Characteristics of igneous rocks that might be useful for identifying and classifying igneous
rocks are Composition, texture, fizz, and foliation, and grain size.
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?
-
The rocks all have the same hardness
scale.
-
All have pointed edges.
-
The rocks come in different sizes and
shapes.
-
The rocks have different textures to
them
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?
-
All share the same hardness scale.
-
Have pointed edges
-
G comes with a lot of chucks out with
holes
-
E has the glassy texture
Rocks Lab 2
GEOL 121
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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Rocks Lab 2
GEOL 121
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
Intermediate 25%-50%
Porphyritic
Granite
B
Intermediate 25%-50%
Phaneritic
Diorite
C
Mafic 50%-75%
Aphanitic
Gabbro
D
Felsic 25%
Aphanitic
Rhyolite
E
Mafic 50%-75%
Aphanitic
Andesite
F
Mafic 50%-75%
Aphanitic
Basalt
G
Felsic 25%
Vesicular
Basalt
5) How confident do you feel in your identifications?
I feel decently confident in my identifications of the minerals.
6) What is still unclear to you about igneous rock classification?
3
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Rocks Lab 2
GEOL 121
What is unclear to me about the igneous rock classification would be the texture of the
rocks?
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?
8) Examine sedimentary rocks K, O, and P:
What are some ways these rocks are similar?
What are some ways these rocks are different?
-
Fine grained
-
P and O seem very fragile
-
P and O have holes to them
-
K seems a lot thicker than the two
9) Examine sedimentary rocks J, L, and M:
What are some ways these rocks are similar?
What are some ways these rocks are different?
-
All have one solid trait of color.
-
All have a thick scale.
-
Fine grained
-
J and L have different textures
-
M had curved edges and holes
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Rocks Lab 2
GEOL 121
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
GEOL 121
Sample
Rock ID
Reasoning
J
Shale
No reaction to fizz
Little bit of sand
K
Sandstone
No reaction to fizz
Sand particles
L
Sandstone
No reaction fizz
Light sand
M
Conglomerate
No reaction to fizz
Lots of sand and pebbles
N
Breccia
No reaction to fizz
Lots of sand and pebbles
O
Limestone
Huge reaction to the Fizz
Sand particles
P
Coal
No reaction to fizz
Fine grained
11) How confident do you feel in your identifications?
I feel very confident in my identifications to the minerals
12) What is still unclear to you about sedimentary rock classification?
What is unclear to me may be the grainsize in classifying the rocks
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?
Characteristics of metamorphic rocks that may be useful for identifying and classifying
metamorphic rocks would be foliation of the rock
14) Examine metamorphic rocks R, W, and X:
What are some ways these rocks are similar?
What are some ways these rocks are different?
-
Thin and crisp
-
Sleek build
-
Thin
-
All three different in appearance
-
All three different in their scales
15) Examine metamorphic rocks T, U, and V:
What are some ways these rocks are similar?
What are some ways these rocks are different?
-
Neutral colors
-
Similar in dimensions
-
V and U are thin
-
T has crystal in a fine matrix
8
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
Light colored quartz
S
Gneiss
Has foliation
T
Schist
ROCKS BREAK ALONG THE SURFACE
U
Phyllite
Dark silicates
V
Slate
Microscopic
W
Marble
Finely crystalline
X
Quartzite
Grains fused together
17) How confident do you feel in your identifications?
I feel very confident in my identifications.
18) What is still unclear to you about metamorphic rock classification?
The rock ID was a bit confusing
10