Rocks and Minerals > Rock Cycle Activities

Sedimentary Rocks: Sedimentary Snack Bars

by Deborah Hanuscin

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Concept: Sedimentary rock formation

Sedimentary rocks are formed when weathering and erosion break down sedimentary, metamorphic, or igneous rocks into small bits, or sediments. These sediments are then transported (by ice, air, water, etc.). Once they have been deposited, the sediments may be buried by other sediments and lithified, or turned into rock, through compaction (pressure caused from the weight of sediments above) and cementation (sediments are "glued" together by minerals that precipitate out of water that was between the sedimentary particles when they were buried).

Objective:

Students will be able to describe how sedimentary rocks are formed.

Materials:

• ½ cup raisins
• ½ cup dried cranberries
• ½ cup dried apricots
• 1/3 cup dried figs
• 1 cup pitted dates
• ½ cup candied orange peel
• ¼ cup candied cherries
• 1 cup chopped walnuts
• 2-3 tablespoons orange juice
• large mixing bowl
• 8" x 8" x 2" baking pan
• margarine (to grease pan)
• grinder or blender
• measuring cups
• large spoon or spatula

Procedure:

1. Show ingredients to students. Tell them that these represent various types of rocks (igneous, metamorphic, sedimentary).
2. Place the "rocks" into the blender. This represents the physical weathering of the rocks into sediments. Ask students what type of rock is formed from sediments (sedimentary). Explain that dissolved minerals are sometimes needed to form sedimentary rocks (add orange juice then mix together).
3. Ask students what happens to sediments before they become rock. Sediment is transported (carry the sediment over to the pan) and deposited (pour into the greased pan).
4. Ask students what happens to sediments once they are deposited (they are compacted). Use a spoon to mash the ingredients down, or cover the "sediments" with wax paper and place a book on top to simulate the weight of overlying sediments.
5. Ask students how long it may take for sedimentary rocks to form (hundreds or thousands of years!). Tell them that their sedimentary snack bars should be ready to eat tomorrow. Cover and refrigerate overnight.
6. The next day, cut the snack bars into squares and observe. You may wish to have students answer the questions below in their science journals.
7. Eat and enjoy!

Questions:

1. What do you notice about your sedimentary snack?
2. How has it changed from the original "sediments" you used to make it?
3. What holds the "sediments" together?
4. How did your "sedimentary rock" get its shape?
5. Explain how sedimentary rocks are formed.

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