Assignment 2 - Igneous & Metamorphic identification & processes-1 (2)
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Raritan Valley Community College *
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157
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Geology
Date
Jan 9, 2024
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docx
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Assignment 2 - Igneous and Metamorphic Rock
Identification
For this assessment, you will be identifying various rocks in much the same way as you did the minerals. You will use the information you learned in this module to complete the charts below.
Instructions:
1.
You will need to use the rock identification charts provided to help identify these rocks. You can enlarge
the picture by clicking on it and dragging the edges.
2.
Complete the rock sample identification charts (linked on canvas) by using the rock sample pictures, the
rock identification chart, and your knowledge from the text and lectures. 3.
Complete the analysis and application section using your knowledge from the text and lectures. 4.
Make sure your name is on the document before saving.
5.
Save the file as: Rocks_Lastname,FirstInitial (example – Rocks_Dunning,C)
Igneous Rocks Samples
Sample #1:
Sample #2:
Sample #3:
Metamorphic Rock Samples
Sample #1:
Sample #2:
Sample #3:
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Igneous Rock Identification Chart (5 points)
Sample #
Composition
Texture
Comments
Rock Name
Example
Quartz/Feldspar
Aphanitic
Mostly pink
Rhyolite
1
plagioclase feldspar
dense and homogeneous
construction and road-building due to its durability
Basalt
2
natural volcanic
glass
glassy
sharp edges
Obsidian
3
volcanic glass
feldspar, augite, and magnetite.
very porous texture
traps gas bubbles
has abrasive qualities
Pumice
Metamorphic Rock Identification Chart (5 Points)
Sample
#
Texture (Foliated
or Non-foliated)
Composition (what you
see in the rock/minerals
present)
Rock
Name
Parent
Rock
Comments
Example
F
Tiny crystals, Shiny surface
Phyllite
Slate
1
Foliated
alternating layers of
different minerals,
primarily feldspar, quartz,
gneiss
granite
used as a
decorative
stone in
mica, and amphibole
buildings
2
Non-foliated
metamorphism of
limestone or dolostone
rocks
marble
limesto
ne or
dolosto
ne
Fizzes in acid
3
Foliated
medium to coarse-grained
minerals such as mica,
chlorite, talc, and graphite
Schist
shale
Very flaky,
layered
Analysis and Application (10 points)
1.
Based on the rock cycle and what you have observed about igneous rocks, what processes help create igneous rocks? (1 point)
Igneous rocks are formed through the process of cooling and solidification of molten rock material, either from
magma (below the Earth's surface) or lava (on the Earth's surface).
2.
Based on the rock cycle and what you have observed about metamorphic rocks, what processes help create metamorphic rocks? (1 point)
Metamorphic rocks are formed through the process of heat and pressure acting on existing rocks. When rocks are buried deep within the Earth's crust, they can be subjected to high temperatures and pressure, causing their minerals to recrystallize and rearrange.
3.
Speculate on how the different processes of the rock cycle relate to the various rock textures. In other words, what role do the various processes (for each rock type) play in determining their textures? (2 points)
In the rock cycle, various processes shape the textures of rocks. Igneous rocks, formed from cooling magma or lava, display fine-grained textures when cooled quickly (like Basalt) and coarse-grained textures when cooled slowly (like Granite). Sedimentary rocks, created from compacted and cemented sediments, have smooth textures when particles are well-rounded and sorted (like Sandstone) and rough textures when particles are poorly sorted (like Conglomerate). Metamorphic rocks, resulting from heat and pressure acting on existing rocks, exhibit foliated textures with visible layers (like Slate) or non-foliated textures without layers (like Marble). These processes influence the unique textures seen in each rock type, showcasing the dynamic interactions within the rock cycle.
4.
As a rock climber you decide you want to climb the Dike Wall at Mammoth Lakes, California. Based on what you know about partial melting and magmatic differentiation, explain the change in rock as you climb vertically off the ground. Include examples of the rock you pass, their mineral assemblages, and their classifications (texture & composition). Then provide an explanation as to why the rocks changed as they did. Assume the basement rock is peridotite. (3 points)
As you climb the Dike Wall at Mammoth Lakes, California, you'll notice a change in the rocks beneath you. The journey begins with peridotite, a coarse-grained rock made of olivine and pyroxene. Moving up, you encounter
gabbro, an igneous rock with plagioclase feldspar and pyroxene. Further, diorite appears, containing feldspar, hornblende, and sometimes pyroxene. Then, there's andesite, a fine-grained rock with plagioclase feldspar and
hornblende, and rhyolite, rich in quartz and feldspar. These changes happen because of partial melting and
differentiation: as the rocks melt partially, they form new rocks with different minerals and textures based on the cooling rate, creating the diverse layers you encounter while climbing.
5.
Now that you climbed the Dike Wall you decide to move over and climb the contact run. Imagine the dike cuts through a layer of limestone, sandstone, shale, and volcanic tuff. Describe what other rocks and mineral assemblages you would find at the “contact” between the dike and surrounding rock layers. (3 points)
At the contact between the dike and the surrounding rock layers, you would find a zone of altered rocks due to the heat from the molten dike. The limestone near the contact might turn into marble, a metamorphic rock, with crystals of calcite forming due to the heat and pressure. The sandstone could become quartzite, another metamorphic rock, with quartz crystals forming in the grains. Shale might transform into slate, a foliated metamorphic rock, due to the pressure, and the volcanic tuff could change into schist, a foliated metamorphic rock, with flattened mineral grains. These transformations happen because the intense heat and pressure from the dike cause the minerals in the rocks to
recrystallize, forming new textures and mineral assemblages at the contact.
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