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Content Benchmark E.8.C.2
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Atmospheric Process and Water Cycle
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Physical Science

Students know rocks at Earth’s surface weather, forming sediments that are buried, then compacted, heated and often recrystallize
into new rock. E/S

Food and rocks probably have little in common unless you are thinking like a geologist. Just as a chef uses a wide array of ingredients to create a dish, nature uses a variety minerals and sediments to create a masterpiece we call a rock. Whether it is combining items to create a dish like coleslaw, or baking ingredients to make a cake, rocks undergo a similar process in their creation.

When liquid rock known as Magma cools at or near the Earth’s surface it forms igneous rocks. On the surface of the earth, rocks are broken down by the forces of erosion. Weathering, both chemical and mechanical, break rocks down into various sediments. These sediments are the raw ingredients of nature. Sediments may combine into newly formed rocks just as they were found in their original form, like a chocolate chip inside a cookie retains its original properties. However, other sediments are buried deep inside the Earth where they may undergo extreme heat and pressure changing form into something brand new, like flour, sugar, butter, and eggs emerge from the oven as a cake. Just as a chef can create many dishes from the same ingredients; nature is able to construct a multitude of different rocks from the same sediments. Therefore, let us explore the rock cycle to further understand the geologic processes necessary to create each type of rock

The Rock Cycle
The Rock Cycle is the term applied to the continuous process that describes how rock material forms, erodes, changes and is eventually recycled. The process is nonlinear, material can move throughout the cycle through erosion, compaction, partial melting or complete melting. There is no set pattern or sequence that must be followed nor a set duration that rocks will remain in one form or another. The three forms of solid rock are sedimentary, metamorphic and igneous.

Figure 1. The rock cycle.

Igneous Rocks
Igneous comes from the Latin word for fire. Igneous rocks, form from the cooling of liquid rock called magma. Igneous rocks are classified by where they originate, either inside the Earth’s crust, intrusive igneous, or on the Earth’s surface, extrusive igneous. Magma, or molten rock, found in the mantle below may move upward toward Earth’s surface where it is forced out of a volcano in the form of lava and ash, solidifying into extrusive igneous rocks (rhyolite, dacite, andesite, basalt). Or, if the magma solidifies beneath the Earth’s surface it forms intrusive igneous rocks such as granite, diorite or gabbro. Igneous rock that forms deep below the surface of the Earth is also known as plutonic.

Figure 2. Examples of Extrusive Igneous Rock Texture. fine-grained Obsidian (left) and coarse-grained Pyroclastic (right).

In addition to being classified by their place of formation, igneous rocks are also classified by their texture and chemical composition. Texture ranges from glassy, such as Obsidian, to the chunky, such as Pyroclastic (see figure 2 above). The rate at which the molten material cools determines the crystal size. Extrusive rocks cool extremely quickly and form very fine-grained (aphanitic) textures, whereas, intrusive rocks which cool slowly result in coarse-grain (phaneritic) textures.

Figure 3.Diorite – medium, course-grained intrusive igneous rock.

Figure 4.Granite – large, coarse-grained intrusive igneous rock.

Figure 5. Igneous Rock chart based on relative mineral content and
environment of formation. (From

Figure 5 above is a chart that shows the classification of common igneous rocks based on their chemical composition, and on their location of formation. Each row on the chart represents the equivalent of 10% composition, however you should note that each of the rock types listed not only has specific minerals that compose them but actually have a range in the percentage of their mineral composition. For example, Granite is composed of quartz (30%-42%), Potash Feldspar (20% - 40%), plagioclase feldspar (5%-35%), biotite (0% - 10%). These variations in composition explain how a given type of rock such as granite can vary greatly in color and mineral content.

Sedimentary Rocks
The sedimentary rock gets its start on the surface of the Earth. Rocks break apart into sediments or fine particles through the process of chemical and mechanical weathering. These sediments are then transported (via the process of erosion) through a combination of forces including; gravity, air and water to a new location. Once they arrive at their “final” destination, they are deposited, settle, compacted and cemented together. It is through this process of deposition, compaction and cementation that forms what we know to be sedimentary rock layers. If you have ever traveled to the Grand Canyon (see figure 6 below) or looked and almost any of the mountain ranges in Nevada, you have seen prime examples of sedimentary rocks. The vast layers that can be observed in a deep canyon or road cuts through mountains are deposits that formed millions of years ago, now exposed by the cutting action of the Colorado River or the effects of crustal movement, and human activity.

Figure 6. The rock layers in the Grand Canyon.
cache/parkphoto _lightbox/files/parkphotos/GRCA_GrandCanyonHDR.jpg

Sedimentary rocks can be further classified into three categories: clastic, non-clastic, and organic. Clastic sedimentary rocks form from the weathering of existing rocks and have a texture made up of clasts, matrix, and cement. The clasts are basically smaller rocks, grains, gravel, or “pieces” that compose the rock. They are encased by the matrix, which is the mud or fine grained sediment surrounding the clasts. Finally this is all bound together by the cement, which is like glue binding all the pieces together. These clastic sedimentary rocks are categorized along a scale by grain/clast size beginning with the finest particles (‹ 0.002 mm) composing the shales, followed by siltstones (particle size 0.002 mm -0.063 mm). Sandstones have a slightly coarser texture with grains ranging from 0.063 mm up to 2 mm in diameter. Clastic rocks with grains between 2 mm and 263 mm are classified as either conglomerates or breccias. Breccias (Figure 8) are composed primarily of angular clastic particles, whereas conglomerates (Figure 9) are composed primarily of rounded clasts.

Figure 7. A diagram showing the sediments that compose the sedimentary rocks after compaction and cementation.(From
/courses/1001/1001_ edwards/web_figures/WebFigures4-1.html

Figure 8. Breccia, note the sharp edged clasts that make up the rock.

Figure 9.Conglomerate, note the rounded edges of the clasts that compose the sample.(From

Non-clastic sedimentary rocks, sometimes called chemical/biochemical sedimentary rocks, are composed of evaporites, carbonates, and siliceous rocks. Evaporites typically form from the evaporation of sea or salt water; examples include rock salt and rock gypsum. Carbonates, such as limestone and dolostone, are composed of the minerals calcite and dolomite and form from both chemical and biochemical processes. Siliceous rocks are made primarily of silica. Chert and diatomite are two examples of siliceous sedimentary rocks.

Figure 10. Limestone can be distinguished from dolostone because it will fizz when tested with weak Hydrochorlic acid (1M HCl).

The final category of sedimentary rocks is the organics, coal being the most common example. Unlike the two other subgroups, organic sedimentary rocks do not contain minerals. Instead they are composed of organic matter, typically from plants. Coals begin as peat, and include lignite, bituminous, and anthracite varieties. Their origin is typically large prehistoric swamps and bogs.

Figure 11. Examples of two types of coal: bituminous coal (left) and anthracite (right) (From

Metamorphic Rocks
The term metamorphosis most likely brings to mind caterpillars turning into butterflies, but if you are a geologist you probably think of rocks. Typically we imagine the changes that insects undergo when we think of the term; however, the term can apply to rocks too. Rocks can change or “morph” from any type into a metamorphic rock if they are subjected to sufficient heat and pressure. Metamorphic rocks form below the Earth’s surface. Any rock type that gets buried deep inside the crust where it can undergo high temperatures and/or extreme pressure can be transformed into metamorphic rocks. Unlike the complete melting that must occur in order for igneous rock formation; metamorphic rocks are not completely melted but only partially melted, resulting in new grain sizes and orientation of the existing minerals. You can see this in the example of slate forming from shale, gneiss forming from granite (Figure 11), or marble forming from limestone.

Figure 12. Granite is the “source” rock for Gneiss, it’s metamorphic offspring.

Metamorphic rocks can form regionally or locally. Heat, pressure, and strain are all processes associated with regional metamorphism. Heat and pressure act together since both increase as the depth below Earth’s surface increases. The Gneiss shown above is an example of rock formed by this intense heat and pressure. Strain refers to any change in the shape of rocks due to the forces of stress. As fluids form and move, new minerals grow with their grains tilted according to the direction of pressure. When strain makes the rock stretch, these minerals form layers. The presence of mineral layers is called foliation and is an important identifying factor when observing metamorphic rocks

Local metamorphism occurs on a much smaller scale than regional metamorphism and normally takes place at shallow levels with low pressure when hot magma comes in contact with surrounding rock and causes alterations. Unlike metamorphic rocks formed by regional metamorphism, contact metamorphic rocks lack foliation.

Figure 13. Example of contact metamorphism. Lava flow baked mud below it into red shale. (From

Conservation of Matter
The rock cycle is nature’s way of recycling to solid portion of our planet. The rocks found by today’s geologists, students, hikers, and other nature lovers are composed of the same materials that have always existed since Earth’s beginning. Over time, rocks are recycled back into the mantle where they are melted and possibly re-solidified to become solid rocks again. This is a continuous process and rocks tend to move through the cycle relatively quickly, geologically speaking. Although, there are a few examples of rocks that are over two billion years old, but most are much younger than that.

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Content Benchmark E.8.C.2

Students know rocks at Earth’s surface weather, forming sediments that are buried, then compacted, heated and often recrystallize into new rock. E/S

Common misconceptions associated with this benchmark

1. Students have difficulty understanding the definition of a rock.

Geologists use the term “rock” to define a category or large mass. When referencing rock, scientists think on a large scale. Whereas, what most people think of a rock, pebble or stone, geologists call a “clast.” Students often believe rocks and minerals are the same thing. They also believe humans can fabricate rocks and minerals. 

For more information about these misconceptions and for strategies to address them, visit the Common Misconceptions about Rocks and Minerals website from Beyond Penguins and Polar Bears at ?
date=September 200& departmentid =profe ssional& columnid= professional!misconceptions

What Is It? Interactive activity can be used to assess prior knowledge,

What Is It? Directions and answer key:

2. Students do not comprehend the geologic scales of space and time.  

Humans view the world through human scales of space and time. It is challenging for students to comprehend the vast nature of geologic time. Although most can quote the age of the Earth, students do not realize the amount of time it takes for the geologic processes responsible for the formation, destruction, and processes in the rock cycle to occur.

For strategies to address this misconception, visit Understanding Geologic Time, an informational tour in which students gain a basic understanding of geologic time, and the significance of the Geologic Time Scale.

See the Teacher’s Guide for an overview and links to lesson plans and interactive student pages at /explorations
/tours/geotime/ guide/index.html

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Content Benchmark E.8.C.2

Students know rocks at Earth’s surface weather, forming sediments that are buried, then compacted, heated and often recrystallized into new rock.   E/S

Sample Test Questions

1st Item Specification: Understand the rock cycle, identify each type of rock (igneous, sedimentary, and metamorphic) and identify the processes needed to create each type of rock.

Depth of Knowledge Level 1

  1. The three rock types are
    1. intrusive, extrusive, and weathered.
    2. igneous, sedimentary, and metamorphic.
    3. volcanic, layered, and igneous.
    4. conglomerate, eroded, and slumped.
  1. Metamorphic rock forms when the structure of pre-existing rock is changed. What processes can change rock in this manner?
    1. Extruding and Cooling
    2. Compaction & Cementation
    3. Weathering & Erosion
    4. Heat & Pressure
  1. The process by which rocks are broken down by water, wind, or ice is
    1. mechanical weathering.
    2. chemical weathering.
    3. biological weathering.
    4. structural weathering.

Depth of Knowledge Level 2

  1. Several rock samples are observed to be visibly layered with similar particle size, color and arrangement.  The rock samples should be classified as
    1. igneous.
    2. amphibole.
    3. sedimentary.
    4. metamorphic.
  1. A sample of basalt has smaller crystals than a sample of granite. What is the most likely reason for this? The basalt
    1. forms when magma cools slowly.
    2. forms when magma cools quickly.
    3. contains lighter elements than granite.
    4. contains heavier elements than granite.

2nd Item Specification: Recognize the processes of the rock cycle.

Depth of Knowledge Level 1

  1. Which of the following does NOT happen in the rock cycle?
    1. Organization
    2. Deposition
    3. Burial
    4. Uplift
  1. Magma is a result of what process?
    1. Cementation
    2. Crystallization
    3. Melting
    4. Metamorphism

Depth of Knowledge Level 2

  1. Use the following diagram to answer the question.


  1. Which two classes of rock will form near or at Earth’s surface?
    1. Extrusive igneous and sedimentary
    2. Sedimentary and intrusive igneous
    3. Metamorphic and igneous
    4. Metamorphic and sedimentary

3rd Item Specification: Understand that matter is conserved in the rock cycle.

Depth of Knowledge Level 1

  1. Throughout the rock cycle many processes take place (weathering, sedimentation, transformation). What happens to the total amount of material?
    1. It stays the same as its form changes.
    2. It increases as its form changes.
    3. It decreases as its form changes.
    4. It fluctuates as its form changes.
  1. When rock material erodes off of a mountain and is deposited in a valley, the total amount of rock, sand and sediments
    1. increases from the amount solid parent rock.
    2. decreases the amount solid parent rock.
    3. remains the same as the amount of solid parent rock.
    4. is unable to be determined.

Depth of Knowledge Level 2

  1. Scientists believe the amount of rock 50 million years from now will be the same as the current amounts. What evidence could be sited for the previous claim?
    1. The total amount of rock on Earth fluctuates greatly.
    2. The total amount of rock on Earth appears to be constant.
    3. The amount of sedimentary rock increases while the amount of metamorphic rock decreases.
    4. The amount of igneous rock increases while the amount of sedimentary rock decreases.
  1. The amount of rock on the earth remains fairly constant, yet the amount of lava and magma fluctuates. What is the BEST possible explanation?
    1. The amount of lava released is so minimal that it cannot be recorded.
    2. The lava is quickly eroded and so does not stay as a rock long enough to be recorded.
    3. Rock is contently being melted and turned back into magma.  
    4. Intrusive igneous rock is not recorded until it reaches the Earth’s surface.

Constructed Response Sample

1. The diagram below represents the rock cycle.


  1. The melting of rocks, below the surface of the Earth produces magma (E).  When magma solidifies, what type of rock (D) can form?
  2. Describe two processes this rock (D) can undergo.  Provide details of where each processes takes place.
  3. What are the results of these processes discussed in part B? Complete the diagram and provide evidence for your answers.

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Content Benchmark E.8.C.2

Students know rocks at Earth’s surface weather, forming sediments that are buried, then compacted, heated and often recrystallized into new rock.   E/S

Answers to Sample Test Questions

  1. B, DOK Level 1
  2. D, DOK Level 1
  3. A, DOK Level 1
  4. C, DOK Level 2
  5. B, DOK Level 2
  6. A, DOK Level 1
  7. C, DOK Level 1
  8. A, DOK Level 2
  9. A, DOK Level 1
  10. C, DOK Level 1
  11. B, DOK Level 2
  12. C, DOK Level 2

Constructed Response E.8.C.2 Score Rubric:

Rock Cycle TIPS.JPG

3 points

Response addresses all parts of the question clearly and correctly.

  1. Diagram is completed correctly.
  2. Processes and locations identified: metamorphism below the earth’s surface under conditions of extreme heat and pressure, along with weathering and erosion at the earth’s surface. Metamorphism is the process in which rocks undergo intense heat and pressure below the earth’s surface resulting in metamorphic rock
  3. Weathering and erosion breakdown rock which is then deposited as sediments that undergo compaction and cementation to form sedimentary rocks

2 points

 Response addresses all part of the question and includes only minor errors.

1 point

Response does not address all parts of the question.

0 points

Response is totally incorrect or no response provided.

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Content Benchmark E.8.C.2

Students know rocks at Earth’s surface weather, forming sediments that are buried, then compacted, heated and often recrystallize into new rock. E/S

Intervention Strategies and Resources

The following is a list of intervention strategies and resources that will facilitate student understanding of this benchmark.

1. Schoolyard Geology, Lesson 2: Rock Stories

This site was developed by the United States Geologic Survey (USGS). In this lesson, students learn that a rock's properties tell stories about where it came from and where it has been. The lesson illustrates how to make geologic observations and gives background about the important properties of rocks to observe. Students then use those observation skills to describe rocks they find on their own Schoolyard. This web site describes specific ’geologic’ features found on playgrounds (with photos and rocks from example schools).

To access lesson plans go to

2. Mineralogy 4 Kids, The Rock Cycle

Developed by the Mineralogical Society of America and selected by the SciLinks program, a service of the National Science Teachers Association. This site includes interactive links to show students the types of rocks found in the rock cycle, provides pictures of rock samples, and a rock identification chart.

To access this activity go to

3. The Rock Cycle (Beyond Books - Earth Science: Part 2)

The Rock Cycle is from Beyond, a highly interactive site with readings, games, experiments, and literacy strategies.

To access readings and activities go to

4. Rock and the Rock Cycle

From Windows to the Universe website the activity “Interactive Rock Cycle” allows students to click on various parts of the cycle to find out about the different rock types. Also provides information on geologic time and plate tectonics. Each page can be viewed in English or Spanish with beginner, intermediate, and advanced levels for each.

To access the website go to edu=elem

5. Rock Cycle: Cycling

This is a free offer from the National Science Teacher’s Association (NSTA). This activity explores the variables that contribute to rock transformation and the continuous processes of rock formation that constitute the rock cycle. It uses recycling as a context for students to comprehend observation of matter in relation to the rock cycle.

To download the free SciPack use the following link: 10.2505%2f7%2fSCB-RK.3.1

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Support Pages

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Benchmark Related Vocabulary

Earth material
Igneous rock
Metamorphic rock
Rock cycle
Sedimentary rock