Activity 7: Rock Cycle

THE SWEET TASTE OF A SUGAR ROCK CYCLE

Summary:

Rocks exist in three phases and change from one phase to another according to the types of mechanical and chemical stresses to which they are exposed. Using common table sugar, students will see how rocks change from one rock type to another when submitted to these different stresses.

Instructional Method:

Demonstration

Goal:

Show students how rock properties change from rock type to rock type due to different processes.

Objectives:
Students will be able to:

• Diagram the rock cycle
• Label the stresses used to cause change between each rock type

Time:

30 minutes

Materials Needed:

• Sugar cubes
• Granulated sugar
• Popsicle sticks
• Paper cups
• Heat source
• Pan to melt the sugar
• Water
• Spray bottle
• Printable rock cycle diagram

Vocabulary:

erosion
heat
igneous
metamorphic
pressure
sedimentary
transport

Background:

All rocks are connected in a cycle of creation, change, and destruction called the Rock Cycle. The rock cycle begins with molten rock (magma below ground, lava above ground), which cools and hardens to form igneous rock. Exposure to weathering and erosional forces, break the original rock into smaller pieces. The smaller material (now called sediment) is carried away by rivers, wind, glaciers, and other means and is eventually deposited elsewhere. These sediments can then be buried and lithified (hardened), forming sedimentary rock.

Sedimentary rock can be deeply buried, subjected to heat and pressure, which over time, cause it to change its structure into a new rock, a metamorphic rock. Metamorphism is a big word meaning change. Eventually, these metamorphic rocks may be heated to the point where they again melt into magma.

Note that the rock cycle doesn't always have to work in this order; sometimes igneous rocks can be buried and metamorphosed, skipping the sedimentary rock phase, and sometimes sedimentary and metamorphic rocks can be uplifted and eroded to form new sedimentary rocks. It is also possible for rocks to remain unchanged in stable regions for long periods of time.

Rocks cycle through three rock types: igneous, metamorphic and sedimentary. The three rock types are connected through processes of erosion, pressure, heating and/or melting.

• Sedimentary rocks form when sediments worn from other rocks are cemented together.
• Metamorphic rocks form by altering the chemistry, mineralogy, or texture of rocks through extreme pressure and/or heat over a long period of time.
• Igneous rocks form by cooling molten rock in the form of magma or lava.

 

The various stresses acting on rocks in the rock cycle are represented by colored arrows that point the direction of the rocks change. The colors of the arrows correspond to the color of their description (ex: all red arrows represent "heat, pressure, chemical activity" which is printed in red).

NPS

 

Instructional Procedures:

1. During the activity, make sure to show the results of each process to the students.
2. Show sugar cubes to students. These can represent sedimentary rock.
3. Crush the cubes forming a powder. This represents weathering in the rock cycle, or the wearing down of the rock into sediments.
4. Pour sugar into a pan. This represents transportation (erosion).
5. Heat the sugar. This is the beginning of metamorphism. Try to point out the change in the rock's appearance (metamorphism) before the crystals actually melt.
6. Heat the mixture to melting or caramelizing. This is melting beyond metamorphism to form lava or magma (igneous rock).
7. Let cool and harden representing igneous rock. Then break into pieces, weathering.
   -
8. To represent sedimentary rocks out of sedimentary rocks use granulated sugar. Pour one cup sugar into a pan and add 1/2 cup water. Stir until dissolved. This is transportation in water.
9. Place a string or stick into the pan and let sit for a few days.
10. Crystals will form on the string or stick. This represents sedimentation due to evaporation and precipitation, which is the same process that forms salt deposits.
    -
11. Another way to demonstrate sedimentary rock from sedimentary rock is to use sugar cubes, representing sedimentary rock, and crush them (weathering).
12. Pour them onto a plate (erosion).
13. Spray the pile with water. Be careful not to spray to much or the grains will dissolve completely!
14. Let dry, you have formed a new sedimentary rock without altering the grain shape.

Discussion:

Ask students what is happening between each 'new' rock; heating, weathering, etc. Before each process tell students what you will do to the sugar and ask them to predict what type of rock will result.

Variation:

If you have rock sugar candy you can begin the experiment with this and relate it to igneous rock.

Included National Parks and other sites:

Big Bend National Park
Bryce Canyon National Park
Black Canyon of the Gunnison
Grand Canyon National Park
Northern Cascades National Park
Sunset Crater Volcano National Monument
Yellowstone National Park

Photos:

Metamorphic Rock at the Bottom of the Grand Canyon
Sedimentary Rock at Bryce Canyon
Igneous Rock at Sunset Crater

Utah Science Core:

2nd Grade Standard 6 Objective 1,2,3
4th Grade Standard 3 Objective 1,2

 

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