Activity Sheet-3
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Bakersfield College *
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Geology
Date
Jan 9, 2024
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Activity Sheet-3 Rocks - Lecture -- 120 points
I
t’s all about relationships. As you prepare for exam-1, review the content below and formulate relationships between basic mineral
chemistry (composition) and textural characteristics of rocks. In many cases, don’t memorize, but explain in your own words and
develop a picture in your mind regarding rocks. Most importantly, as you learn the concept and relationship, be able to explain the
concept using the proper terminology. Please make sure you take a look at the probable exam essay questions at the end of this
activity sheet. It’s recommended that you view the rock lecture in its entirety before answering questions.
1.
Elements make minerals, and Minerals make rocks.
Relationship questions:
a.
Explain how a rock is different than a mineral
●
A rock is composed of several minerals when elements are combined to form minerals.
b.
Write a definition of a rock ---- in your own words
●
A rock is composed of several minerals and it can fall under the category of igneous, sedimentary, or metamorphic.
c.
Does the 5-part definition of a mineral fit the definition of rock? Why or Why not?
●
No, it does not fit under the definition of a rock because the 5 part definition is primary for its crystalline structure and rocks do
not have that crystal structure.
2.
Briefly, write your own definition of an igneous, sedimentary and metamorphic rock.
●
Igneous rocks are formed by magma or lava. Sedimentary is formed off of intense weathering processes that has been
compressed and hardened by the earth's surface
Relationship questions:
a.
What criteria allow scientists (geologists) to divide rocks into three categories?
●
Geologists focus on the texture and composition of rocks
b.
How does each rock group relate to the rock cycle?
●
Igneous rocks are formed at the beginning of the cycle as soon as magma cools down and solidifies. Sedimentary rocks can
be formed by igneous rocks if it's compressed and cemented to form a new rock. Metamorphic rocks can be formed by either
igneous or sedimentary rocks if they are heated and pressurized to form a new rock.
3.
Identification of rocks (igneous, sedimentary, metamorphic) is made by observing the rock's textural characteristic and its
composition.
●
Relationship questions:
a.
Define Texture and Composition (IMPORTANT ROCK CONCEPTS)
●
Texture:
○
The appearance of the rock
○
Size shape and arrangement of mineral grains
●
Composition (mineral assemblages)
○
Types and relative proportions of minerals making up a rock
○
Composition, mineral makeup, and chemistry are all indicators of a rock’s composition
b.
Draw a diagram illustrating how a geologist views the term texture when identifying a rock
c.
Draw a diagram illustrating how a geologist views composition when identifying a rock
d.
What geologic conditions control textural characteristics for each rock group?
●
It requires temperature, time, and space are some reasons that control the texture of these rocks. If a rock cools too quickly, it
will have a finer grain size. If it cools slowly that means there will be more time for minerals to form larger crystals inside the
rock
Igneous Rocks
4.
Igneous rocks are classified as either intrusive or extrusive.
Relationship questions:
a.
Define intrusive and extrusive as it relates to igneous rocks
●
Extrusive igneous rocks are cooled above the earth’s surface. Intrusive igneous rocks are cooled BELOW earth’s surface
b.
How do textural characteristics differ between intrusive/extrusive igneous rocks? Draw a diagram
c.
Using the terms phaneritic and aphanitic, label your diagram and explain the geological environment
producing these textures.
5.
Compositions of igneous rocks can be identified based on the color of the rock (light, dark or intermediate colors)
Relationship questions:
a.
What mineral compositions typically color the igneous rock dark, light and intermediate?
●
Dark rocks are usually formed of dark minerals such as olivine and pyroxene. Light rocks are composed of light minerals such
as quarts and feldspar. Intermediate rocks that have a composition of a low-density mineral such as feldspar and a high
density mineral which is quartz
b.
Describe the terms mafic and felsic with respect to mineral compositions of igneous rocks
●
Mafic rocks are dark-composition rocks with high-density minerals like magnesium. Felsic rocks are light-composition rocks
that are composed of low-density minerals like silica
c.
Mafic compositions are known for high concentrations of
Magnesium and iron
d.
Felsic compositions are known for high concentrations of
SIlica
6. Classification of igneous rocks is based on texture and composition. Use the igneous rock classification chart and fill the blanks
below.
a.
A phaneritic felsic igneous rock is identified as a
Granite
b.
An aphanitic, felsic igneous rock is identified as a
Rhyolite
c.
A phaneritic, mafic igneous rocks is identified as a
gabbro
d.
An aphanitic, mafic igneous rock is identified as a
Basalt
e.
A phaneritic intermediate igneous rock is identified as a
diorite
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f.
An aphanitic intermediate igneous rocks is identified as a
Andesite
Relationship questions
1.
Describe the relationship with rocks A and B , C and D and E and F. (What is similar)
●
Granite and Rhyolite are both light rocks composed of at least 70% silica. Gabbro and Basalt are both composed of most 50%
silica. Diorite and Andesite are both composed of 60% silica
2.
Describe the differences in the geologic environment with rocks A/B, C/D and E/F (What is different?)
●
Rocks A, C, and E are intrusive igneous rocks so they are cooled under the earth’s surface. Rocks B, D, and F are all
extrusive igneous rocks that are cooled above the earth’s surface.
Sedimentary Rocks
7. Sedimentary rocks are formed from the weathering process within the “sedimentary rock cycle”. Define
each term in the sedimentary cycle and arrange the terms in order that would result the formation of a
sedimentary rock
1.
Lithification -
Sediment becomes compacted or cemented together
2.
Weathering-
Pre-existing rocks are worn down by the wind, water, ice, etc
3.
Deposition -
Sediment is deposited after being transported
4.
Transportation
- Unconsolidated sediment moved by wind, water, etc
5.
Unconsolidated sediment-
Loose sediment EX sand
6.
sedimentary rock -
sediment is compacted and becomes a rock
8. Sedimentary rocks are divided into 3 categories based on the type of sediment. Rather than memorize each
category, provide a one to three word description of each category that clearly shows the difference
a.
Detrital (clastic)-
Rock with rock
b.
Chemical -
Mineral sedimentary rock
c.
Organic (bioclastic) -
Plant Sedimentary rock
9. Using your answers in #8, refer to the rock lecture and identify the common sedimentary rocks that have
been lithified.
Detrital: (Name the rock types according to decreasing grain size)
Conglomerate, sandstone,
siltstone, shale
Chemical:
Gypsum, halite, limestone
Organic:
Chalk, Fossil limestone, Coquina
Relationship questions:
1.
Describe the textural differences between detrital, chemical and organic sedimentary rocks
●
Detrital sedimentary rocks have decreasing particle sizes ranging from Pebbles to Flour sized grains.
Chemical sediments are precipitation processes. Organic sedimentary (animal parts) rocks will always
have fossils or parts of shells.
2.
Why is hydrochloric acid (HCL) a useful test for chemical sedimentary rocks?
●
Chemical sediment rocks react with hydrochloric acid and it will show its effectiveness if it was calcium
carbonated cemented rock.
3.
Can organic and chemical sedimentary rocks react with HCL Why?
●
No, they cannot react with HCL, they will most likely break down and dissolve.
4.
What does detrital, chemical and organic sedimentary rocks tell the field geologist about ancient
geologic environments?
●
A geologist can determine the minerals in a sedimentary rock at one point in time. If the sediment rock
have plant or animal fossils, then they can determine what type of life that lived there. If the rock it
mostly dry in that area, then it could be evidence that there was water somewhere close.
Metamorphic Rocks
1.
Based on your first viewing of the rock lecture, write a brief sentence describing the general differences
between igneous and metamorphic rock textures--- What do you observe?
●
Igneous rocks have a lot of visible grains, metamorphic rocks have no grains.
2.
What is a good working definition of a metamorphic rock (refer to the lecture)
●
It would be the transformation of pre-existing rock into a metamorphic rock through a pressure and
temperature relationship.
Relationship questions:
a.
What is meant by “solid-state-transformation?”
●
When a rock is in between a solid and a liquid state when it changes from a pre-existing rock to a
metamorphic rock
b.
How would the metamorphic rock be classified if temperatures turned the rock into a liquid?
●
It would be considered as magma if the rock turned back into a liquid
c.
What depths (pressure) and temperature is considered for preexisting rocks to begin
metamorphism?
●
Metamorphism happens around 5km below the earth’s surface and at a temperature of 150 degrees
celsius
Metamorphic rock geologic environments
1.
Contrast the differences between contact and regional metamorphism on pre-existing rocks. Draw a
diagram that represents contact and regional metamorphism.
●
In summary in metamorphism, Magma comes into contact with solid rock. The heat from the magma is
transferred and the solid rock is changed and this change happens quickly. In regional metamorphism,
Pre-existing rock is put under intense stress like the force that makes mountains. This change happens
slowly over time.
Relationship question;
1.
If you understand the condition for one type of metamorphism, how would you use the
conditions to learn the other type of metamorphism (contact vs. regional)
●
The word regional suggests something that is taking place in a specific location. Regional
metamorphism takes place in an area of high stress on the earth. Contact metamorphism takes place
when the rock comes into contact with molten rock.
10. The geothermal gradient provides another type of heat source for metamorphism.
1.
Observing the geothermal gradient diagram, what is the geothermal gradient telling you
regarding the y-axis and x-axis?
●
The y-axis Is the temperature below the earth’s surface measured in celsius. The x-axis is the depth
below the earth’s surface measured in kilometers.
2.
Fill in the blanks ---- As depth increases,
Pressure
increases, and
Temperature
increases.
Relationship questions:
1.
If temperature was increased at a constant rate, what would the temperature gradient line look
like on the geothermal gradient graph?
●
If the temperature was increasing at a constant rate, then there would be a straight diagonal line going
down as depth and temperature increased.
2.
At what depth does the geothermal gradient rise rapidly and what depths does the geothermal
gradient become less?
●
About 1000 km below the earth’s surface, the geothermal gradient rises rapidly. After reaching 2000 km
below the earth’s surface, the gradient slows down and the temperature rises very slowly.
3.
Why is the geothermal gradient rapid in the upper part of the earth’s interior?
●
It is rapid in the upper part of the earth’s interior because the cool rock is heated as depth increases
11. As earth depth increases, pressure increases. Pressure on rocks is variable but can exist between two
end members ---- from confining to differential type pressures.
1.
Define confining and differential type pressures
●
Confining pressure is equal amounts of pressure on all sides of the rock. Differential pressure is the
different amounts of pressure on each side of the rock
2.
Provide an example of confining and differential pressure
●
Confining pressure is a rock with minerals that have been lithified (compacted). An example of
differential pressure would be a rock that has bands of minerals through it
Relationship questions:
1.
During metamorphic processes, which type of pressure do you think is dominant and why?
●
Differential pressure is dominant because it is more likely that rocks are subjected to varying amounts
of pressure
2.
Describe some common metamorphic environments that would produce enough pressure to
deform solid rock
●
A common metamorphic environment would be two tectonic plates converge
3.
How is the statement “solid-state-transformation” related to pressures deforming rock?
●
The rock is still solid but is malleable enough to transform
12. Remember that identification of rocks is a function of textural and compositional characteristics. In
metamorphic rock textures, geologists use the term foliation and non-foliation for identification.
1.
Define the textural terms “foliated” and “nonfoliated”
●
Foliated means layers that present in rocks after being subjected to extreme pressure coming from one
direction. Non-foliated refers to metamorphic rocks that do not have obvious layers.
2.
Provide metamorphic rock examples for foliated and nonfoliated types.
●
Foliated metamorphic rocks include slate and schist. Examples of non-foliated metamorphic rocks
include quartzite and marble.
Relationship questions:
1.
What is the pressure/temperature relationship difference between the rocks gneiss and slate?
●
Genesis is a metamorphosized rock that is formed under extreme temperature and pressure. Slate is
metamorphosized shale that has not been placed under the same conditions as the genesis
2.
How does grain size tell the geologist if the rock was subjected to high or low metamorphism
temperatures and pressure?
●
A rock that has been placed under a lot of temperature and pressure will have a greater chance of
having a foliation and or minerals that are more stable in these extreme environments. The more
foliation or minerals present, the more it can mean the rock was undergoing more extreme conditions.
3.
If pressure and temperature conditions are great enough to exceed the
solid-state-transformation state and the rock material becomes liquid, what part of the rock cycle
is represented? And how does this define the “rock cycle”?
●
If the rock material becomes liquid, then it is considered magma. Magma can then harden into igneous
rock and the rock cycle can continue.
Possible essay questions
1.
Define the differences between contact and regional metamorphism and provide two examples of
metamorphic rock types
●
Contact Metamorphism means the contact of magma of solid rocks meaning that heat is transferred
into an overlying rock, changing the pre-existing rock. It is also very fast acting like cooking an egg in a
frying pan. Some rock examples are marble and quartz formed within the metamorphism.
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●
Regional metamorphism starts with deformation and is subjected to intense stresses and strains. The
process is high heat with high pressure. Two metamorphic rocks rock types examples are Genesis and
Schist.
2.
Briefly explain the formation of each rock type (igneous, sedimentary, metamorphic) and provide three
rock examples for each rock group.
●
Igneous rocks are formed by solidifying molten hot lava in order to form an igneous rock. This process
can happen above or below the earth’s surface. If some igneous rocks are subjected to any weathering
processes then it becomes sedimentary rock. Some examples of igneous rocks are diorite, gabbro, and
granite
●
Sedimentary rocks are formed on the earth's surface from the weathering processes. For example, if
any pre-existing rock is on the surface and it undergoes the weathering process such as ice, rain, wind,
or hail then it is considered a sedimentary rock. Some common examples of sedimentary rocks are
sandstone, limestone, and shale
●
The process of a rock being considered a metamorphic rock is when a pre-existing rock is below 5km
below the earth’s surface and exposed to rising pressure and temperature. If the rock becomes a liquid
then it is considered magma. Magma can then be hardened into igneous rock and the rock cycle can
continue.
3.
How is the rock cycle related to internal and external forces?
●
Internal earth forces are things that happen within the earth, this includes the cooling of rocks within the
earth. Earthquakes, moving continents, the elevation of mountains, and volcano eruptions are
considered to be a part of the earth’s interior. The way internal forces interact with the rock cycle is by
the volcano eruption, rocks from the earth’s surface are able to be exposed to the oxygen on the earth’s
surface, which can continue the rock cycle.
●
Earth’s external forces are processes that happen on the earth’s surface such as the hydrosphere,
atmosphere, and erosion. The interaction between the earth's external force and the rock cycle is that
the cooling process happens above the earth’s surface in order for it to become a sedimentary rock.