Lab 6 Metamorphic Rocks
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Northeastern University *
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MISC
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Geology
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Apr 3, 2024
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Name: ________________________________________________ Score: ____/50 Lab 6 – Metamorphic Rocks Part A: Diagnostic features of Metamorphic Rocks (9 pts) 1. What index mineral appears when shale (non-metamorphic) becomes slate (metamorphic)? How large are these crystals? (1 pt.)
The index mineral that appears when shale becomes slate is chlorite. The crystals of chlorite are microscopic. 2. What index mineral transformations occur when slate becomes phyllite or schist? How large are the crystals? (1 pt.)
The index mineral that appears when slate become phyllite or schist is biotite. The crystals are macroscopic. 3. What index mineral transformations occur when schist becomes gneiss? What happens to the mafic and felsic minerals in the rock? (2pts.)
The index mineral that appears when schist becomes gneiss is potassium feldspar. The mafic and felsic minerals in the rock become segregated at this high grade of metamorphism. 4. What is the difference between the mineral crystals in limestone and marble? Both rocks are effervescent when exposed to dilute acid. (1 pt.) The crystals in marble are larger than the crystals in most limestones. 5. What kinds of sedimentary features can be retained through the metamorphic process and still be seen even after the sedimentary rock has been metamorphosed? (1 pt.)
Sedimentary structures like bedding, cross bedding, and ripples from the protolith are can be preserved in the metamorphosed rock. 6. Shales have an interesting progression through the metamorphic sequence (slate, phyllite, schist, gneiss), but for quartz sandstone it is more boring—it just becomes quartzite. Why is this? (1 pt.) Quartz sandstone has less mineral transformations because sandstones are dominated by quartz, which is generally stable across all pressure and temperature conditions. 1
7.
As you are working your way through Part B, take a photograph of a foliated rock and use annotate the image to show the direction of maximum pressure and the orientation of the foliation. (2 pts.) Part B: Metamorphic Rocks Identification (2 pts per rock; Total: 22 points) Below you will find a table with 11 metamorphic rocks. Use the hand samples, the descriptions above and the information from the presentation at the start of the lab to complete the table below. You can use external websites if you want, but I do not think it will be necessary. Sample
Foliated? (Yes/No)
Segregation? (Yes/No)
Mineral information (i.e., index minerals, microscopic or macroscopic) Rock name
4 No
No
Microscopic grains with chunks of reddish-black rock, dark and light, slightly shiny Metaconglomerate
13 Yes
No
Microscopic grains, red, dull Slate
20 Yes
No
Macroscopic grains, shiny, dark and light minerals
Schist
31 Yes
Yes
Macroscopic grains, shiny, dark and light minerals
Schist
85 Yes
No
Microscopic grains, slightly shiny, grayish-brown color
Phyllite
2
Maximum Pressure
Orientation of Foliation
93 No
No
Microscopic grains, pink, shiny
Quartzite
95 No
No
Microscopic grains, shiny, black
Anthracite coal
IDM U3 No
No
Fizzes readily with dilute hydrochloric acid.
Marble
IDM 23 Yes
Yes
Microscopic grains, brownish-black, dull
Gneiss
RR-15 Yes
Yes
Small visible grains, white and black, mostly due with some shiny grains
Gneiss
S95-2 Yes
Yes
Macroscopic grains, shiny, dark and light minerals
Schist
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Part C: The Rock Cycle (17 pts) 1. Find Mount Rainier on a map. A. Where is this volcano located, both geographically and tectonically? (2 pts.)
The volcano is located in Washington state and sits on the Juan de Fuca plate boundary. It was formed by the subducting of the Juan de Fuca plate under the North American Plate. B. Most of you have probably not been there, but what do you think is a common rock type on the sides of this mountain? Explain your thinking. (2 pts.) I believe andesite could be a common rock type on the side of this mountain as it is an intermediate mineral. Mount Rainier is a stratovolcano and stratovolcanoes commonly produce intermediate materials in their eruptions. 2. Find Fagradalsfjall on a map. A. Where is this volcano located, both geographically and tectonically? (2 pts.)
The volcano is located in Iceland and sits on the Mid-Atlantic Ridge. It was formed by the diverging of the North American and Eurasian plates. B. Most of you have probably not been there, but what do you think is a common rock type on the sides of this mountain? Explain your thinking. (2 pts.) I believe basalt could be a common rock type on the side of this mountain as it is a mafic mineral. Fagradalsfjall is a shield volcano and shield volcanoes commonly produce mafic materials in their eruptions. 3. Imagine a situation where tectonic forces are lifting crust upward. Initially an area is quite deep under the sea, with a water depth of a few hundred feet, but over time the water depth decreases with the uplift until the water depth is zero and the area is right at the shoreline of the ocean (i.e., it is now the beach). A. How will the type of sediment deposited in this area change as the water depth decreases? Name three potential rock types that this sediment would become once it is lithified. (4 pts.) The sediment to begin with will perhaps be mud and as the the water depth decreases the sediment may change to sand and then calcified organisms. The potential rock types that this sediment would create are mudstone, sandstone, and limestone. B.How might your last rock type be different depending on whether this is in a tropical environment as opposed to a cooler environment? (2 pts.) Limestone does not appear in colder environments than tropical or sub-tropical so it would not form in a cooler environment. 4
4. If the rocks you listed in 3A were to be metamorphosed, what would their new names be? (3 pts.)
Mudstone would metamorphose into shale, sandstone would metamorphose into quartzite, and limestone would metamorphose into marble.
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