Our Changing Earth
Lesson 3: How Rocks Change
1. Identify Desired Results
Science Standard 5.2.A.3 - Explain how rock is formed from combinations of different minerals and that
smaller rocks come from the breakage and weathering of bedrock (solid rock underlying soil components) and
larger rocks; soil is made partly form weathered rock, partly form plant remains-and also contains many
living organisms.
Big Ideas:
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Rocks are made from a variety of Earth’s materials.
Unit Essential Questions:
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How does the Earth’s surface change?
Learning Objective: As a result of this lesson, students will know and be able to . . .
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Students will identify and describe the process that forms rocks.
Vocabulary:
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rock cycle – the process of rocks changing into other kinds of rock.
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sediment – broken up pieces of soil, sand, rocks, and the remains of organisms.
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sedimentary rocks – rocks that are formed when sediments are pressed and then cemented together
Materials:
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craft sticks (1 per student)
crayons
Exacto knife (for teacher use)
foil or paper cupcake liners
plastic bags (1 per student)
“Rock Cycle Diagram”
rock Samples (conglomerate, obsidian, quartzite - for each group)
“Which Rock is Sedimentary?” exit pass
Teacher Background:
This lesson is focused on allowing students to see how rocks are formed by weathering and erosion. It is not
necessary for the students to learn the entire rock cycle. Rather, teach the students the general idea of the rock
cycle and how that helps to create our different types of rocks. Prior to the beginning of the lesson, please label
conglomerate as rock 1, obsidian as 2, and quartzite as 3.
2. Assessing Student Learning
Formative: “Which Rock is Sedimentary?” exit pass
Summative: Our Changing Earth final assessment
3. Lesson Elements
Process:
I. Engage: Display the rock cycle diagram on the board. Have students look at the rock cycle diagram and
then pass out the 3 labeled rocks (conglomerate, obsidian, quartzite) to each group. In groups, have
students predict where each rock might belong in the rock cycle. In their journals, have students justify
their predictions. Have students share their predictions.
II. Explore: 1. Distribute a crayon to each student (varying colors within each group). Explain that this “rockcrayon” type (igneous) represents a rock cooled from under the Earth’s crust. Instruct the students to
examine the “rock-crayons” and describe their properties. Key observations of this “rock-crayon” type are:
small holes produced from air bubbles upon cooling, one uniform substance, and smooth (almost glassy)
luster. 2. Next, students will “weather” the rocks with craft sticks into small bits (shavings). Students
should shave as much as they can manage in about 10 minutes. 3. Instruct students to place the crayon
“sediments” into the plastic bags and add pressure, such as by pressing the bag with their hands. After the
students get the crayon sediments to stick together, they should take out the newly formed types of
“rock-crayon” (sedimentary) and describe this rock type. Key observations of this rock-crayon are: visible
pieces of rock fragment/particles, possible stratification (visible layering), not as hard (more brittle) than
the first “rock-crayon” type. 4. For the next “rock-crayon” type, add heat. Working in groups, instruct
students to form a small cup with a handle using the foil. The bottom of the cup should be about 3 cm in
diameter. Students should place sediments and sedimentary rock pieces into the cup and melt them
together using the hot plate, creating the third “rock-crayon” (metamorphic). (It is important to remove
the cups from the heat as soon as the crayons melt!) If a hot plate isn’t available, use small paper cupcake
liners and place in the microwave using a low setting (make sure the crayons do not burn, turn black, catch
on fire, etc.; DO NOT place foil in the microwave.) Let the melted crayon cool and solidify (the layers of
“sediment” should melt together but the different colors should be visible). 5. After students remove
these “metamorphic crayons” from the cups, the teacher can slice up the rock-crayon pieces with a razor
blade/ Exacto knife so that the inside can be viewed. Students now make key observations of this rockcrayon type that might include: no individual particles seen, but rocks contain many different substances;
colors may be swirled together rather than layered or chunked; “rock-crayon” hardness is increased
(compared with the sedimentary rock).
III. Explain: 1. Rocks are formed through weathering and erosion. Rocks are weathered (broken down into
smaller pieces of rock) into sediments and then are carried away by the agents of erosion. These
sediments will then be deposited in a new location where these tiny bits of rock will later join with other
materials (organic materials, other rocks, or shells). Over time, these rocks will undergo changes to their
physical and chemical make up depending on the type of rock that is formed. 2. Sedimentary rocks are
formed on or close to the surface of the Earth. Slowly, different sediments will be pressed together and
then cemented to form sedimentary rocks. 3. Show students the properties chart. 4. For further
investigation into sedimentary rocks, you could show the students the interactive sedimentary rock page:
http://www.fi.edu/fellows/fellow1/oct98/create/sediment.htm
IV. Evaluate: Students will evaluate the 3 rock samples again to determine which of the 3 rock samples is an
example of a sedimentary rock. The students may use the properties of rocks chart to help them identify
the correct rock. Students should record their responses on the “Which Rock is Sedimentary?” exit pass.
V. Extend:
Students could bring in rocks from home to share with the class. They could use the properties of rocks
chart, as well as the Rock Database to help them name and classify their rocks.
Types of Rocks Powerpoint Find out more about the three types of rocks, and see pictures. Students can
test their knowledge at the end.
If Rocks Could Talk - Limestone and If Rocks Could Talk - Sandstone Have a “conversation” with a
sedimentary rock.
Formation of Sedimentary Rocks Watch a short video clip of a sedimentary rock being formed. It might be
helpful to pause the video at the formation stage so that students can clearly see the factors that
contribute to the formation.
4. Reflections
Student Learning Expectations:
Did students achieve the stated objective? How do you know? If not, why not?
Implementation:
How effective was the lesson? What went really well? What would you differently?