Learning About Rocks


Students will:

  • become familiar with the names of the different types of rock
  • explain how the different types of rocks are formed
  • create examples of the different types of rocks


  • Different samples of igneous, metamorphic, and sedimentary rocks
  • Almond bark
  • Candy molds (or aluminum foil made into small containers to hold melted almond bark)
  • Peanut butter (be careful of allergies) or Jelly
  • Graham crackers (2 for each student)
  • Colored taffy (3 pieces for each student)
  • Waxed paper


There are three main types of rock: sedimentary, metamorphic, and igneous. For additional information about these rocks, check out the USGS webpage https://geomaps.wr.usgs.gov/parks/rxmin/rock.html

Sedimentary rocks are the result of the accumulation of small pieces of rocks or sediments such as sand, shells, or pebbles. Gradually, they accumulate in layers and over a long period of time harden into rock. Sedimentary rock is fairly soft and may break apart or crumble easily. It is can contains fossils. Examples of this rock type include limestone and sandstone.

Metamorphic rocks are rocks that have changed or "morphed" into another kind of rock. They're formed from igneous and sedimentary rocks that are subjected to high temperature or pressure or some type of chemical reaction. This causes the rocks' crystal structure to change. Examples of metamorphic rocks: Limestone becomes marble, shale becomes slate, and granite becomes gneiss.

Igneous rocks originate from the cooling and solidification of molten rocks. Igneous rocks can be formed under or above ground. Underground, the molten rock is called magma. As the magma cools underground it becomes igneous rocks, often a form of granite. When the magma rises above the earth surface such as when a volcano erupts, lava is formed. Examples of this rock type include quartz, granite, pegmatite, pumice, obsidian, and lava.

Blindfolded Rock Pass
Have students sit in a large circle blindfolded.
Pass around various types of rocks such as sandstone, limestone, granite, quarts, and have them feel them. These rocks are going to have a different feel to them. Sandstone will be the roughest and mica the smoothest.
3. Tell the students that the rocks feel different because they were formed differently. Have the students notice the difference in weight and structure of the rocks. Sandstone and limestone are made up of many tiny different particles. These rocks are more easily eroded or carved than the smooth granite and quartz rocks.
4. Review the difference between igneous, metamorphic, and sedimentary rocks. Sandstone and limestone are sedimentary rocks. Quartz and granite are igneous. Marble is metamorphic.

Watch the Making of Limestone

Instructional procedure: Tell students that Wind Cave is formed in limestone and they are going to learn how limestone is made. This 10 minute video is available on Wind Cave National Park website: https://www.nps.gov/wica/photosmultimedia/cave-video-clips-and-programs.htm

Edible Rocks Activity:
Tell the class they are going to do an activity showing how the three types of rock are formed.
Divide the students in groups of four.
3. Give four candy molds sprayed with cooking oil and a plastic spoon to each group. For the first part of the activity, allow the class to gather around the table as you melt the almond bark in a pan on the hot plate. Tell the students that the melted chocolate represents magma.
4. Have them return to their groups, and take the container of "magma" to each group. Allow the students to spoon the melted mixture into their candy molds.
5. While their "igneous rocks" cool, distribute the materials to make sedimentary rocks (peanut butter, crackers, knives), and metamorphic rocks (taffy, waxed paper). The students make cracker and peanut butter stacks to illustrate the layers in their "sedimentary rocks".
Each student should then take three pieces of different colored taffy, unwrap them, and stack them on a piece of waxed paper. The student then places the other piece of waxed paper on top of the stack and presses down hard to make "metamorphic rock".
7. To complete the activity, call out the type of rock and have the students hold up the correct rock model they made. Then they can then eat their rock creations.

Discussion Questions:

  • How can an old rock become a new rock?
  • How is metamorphic rock formed?
  • How are sedimentary rocks formed?
  • How are igneous rocks formed?

Last updated: April 10, 2015

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