HOmework for week 3-Rocks
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El Paso Community College *
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Geology
Date
Dec 6, 2023
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docx
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Uploaded by essm8163
Name: Elmer Saenz
Homework Assignment For Week 3- Rocks
For the first six questions of the homework, in a thought experiment, you will compare the
texture of cookies to the textures of igneous rocks. First think of a plain oatmeal cookie (without nuts,
raisins, chocolate chips, etc.) and an undecorated gingerbread cookie. The grain (mineral) size of igneous
rocks is the size of the minerals in the rock. For now, we will just worry about: 1) Minerals that you can
see and 2) areas of rock where you can’t see any minerals (this is called the matrix). The grain size of
igneous rocks can be used for two purposes: 1) to determine if the igneous rock was formed inside or
outside of the earth and 2) to help identify the igneous rock.
1.
Which cookie has individual “minerals” that you can see?
Minerals that I can see would be in a Chocolate Chip Cookie
2.
In which cookie can you NOT see individual “minerals”?
I think in a Plain Oatmeal Cookie.
3.
Which cookie is most similar to an INTRUSIVE igneous rock?
Molten rock (magma) under the surface of the Earth solidifies to produce an intrusive igneous rock.
Due to the gradual cooling of these rocks, bigger mineral crystals might develop. The "Lava Cookie" is
perhaps the cookie that is closest to it in terms of texture and cookie formation.
4.
Which cookie is most similar to an EXTRUSIVE igneous rock?
The most similar cookie in terms of texture and formation process to an extrusive igneous rock would
likely be a "Snap Cookie".
5.
Now think of a chocolate chip cookie. Is this cookie “rock” intrusive or extrusive? Why? (You must
explain why for credit.)
Due to the way it solidified, it would most closely resemble an extrusive igneous rock. The cookie
would probably have a fine-grained texture comparable to rocks like basalt or andesite because it
would have to cool rather quickly after being exposed to the Earth's surface. This fits the traits of
extrusive rocks, which develop from lava that rapidly cools.
6.
In the above example, if the chocolate chip cookie were an igneous rock, what would the chocolate
chips be called?
I think that the chocolate chips could be metaphorically referred to as "inclusions" or "phenocrysts."
7.
You are hiking in the Franklin Mountains and find a conglomerate containing mostly large clasts of
other rocks and a well-sorted sorted sandstone containing mostly quartz grains. Which of these two
rock types had its materials come from a source further away? How do you know that?
Compared to the well-sorted sandstone containing predominantly quartz grains, the conglomerate with
huge clasts of various rocks came from a source that was probably farther away. This is so that
conglomerates, which are produced by the deposition and lithification of larger, more angular
sediments carried by high-energy forces like rivers or swift water, can form.
8.
Metamorphic rocks are not as commonly exposed on Earth’s surface as sedimentary or igneous rocks.
Why do you think this is so?
I think these would be because, the relative rarity of exposed metamorphic rocks is a result of the
specific geological conditions required for their formation, as well as the less frequent occurrence of
the tectonic processes that bring them closer to the surface.
9.
Weathering is part of the rock cycle. Think about the two types of weathering – chemical and physical
weathering. What type of weathering do you think is most likely to happen here in El Paso?
In El Paso, both chemical and physical weathering processes are likely to occur, but I think due to the
arid climate and specific geological characteristics we have here, physical weathering is likely to be
more prominent.
10.
The clasts in sedimentary rocks are often cemented by quartz or calcite. Of calcite-cemented or quartz-
cemented sedimentary rocks, which would be the easiest to erode? (Remember back to the last chapter
on minerals–which mineral is harder, quartz or calcite? What would that say about the strength of the
rock and how easily it might erode?
Quartz is harder than calcite. In terms of the Mohs scale of mineral hardness, quartz ranks 7 while
calcite ranks 3. This means that quartz is more resistant to abrasion and is less likely to erode compared
to calcite. Considering this, a sedimentary rock that is cemented by calcite would be easier to erode
compared to one that is cemented by quartz. Why? Well because the calcite cement would be softer
and more susceptible to weathering and erosion processes. Over time, water, wind, and other natural
forces would more easily break down the calcite-cemented rock compared to a rock with quartz
cement.
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