Learning Experience 4: Sedimentary Rock

TEACHER’S GUIDE

Materials:

For each group of three students:

3 Student Activity Sheets for Learning Experience 4 (Please see PDF)

Caribbean sand

3 pairs of safety goggles

Quartz sand

Glacial till

Clothespin

Epsom salt

4 2 oz plastic cups

4 plastic spoons

Dropper bottle of hydrochloric acid

3 medicine cups

Paper clip

Kite string

Petri dish

Double lens magnifier

Paper towel

White copy paper

For the class:

3 clear plastic tubes

Caribbean sand

Quartz sand

Glacial till

Medicine cup

Hole punch

Stapler

Water

Chart paper

Felt tip markers

Preparation:

Read the background information in the Rocks, Minerals, and Landforms Teacher’s Manual. (Please see PDF)

Session 1

Students will observe and record properties of various sands.

Students should observe how the larger particles fall to the bottom of the tube while the finer portions settle at the top of the sediment. The higher the density of the particles the faster the particles settle. Allow the sand in the tubes to settle completely. Time how long it takes for the sediment for each tube to settle. Chart the time for each tube.

Students can draw a picture of each tube on their activity sheet for Learning Experience 4 in Rocks and Minerals and Landforms Student Activity Book. (Please see PDF) Have students describe how the sand/till has settled.

Session 2

This teacher demonstration will utilize three clear plastic tubes with 30 cc sand samples and 150 cc of water. The teacher will shake the tubes and place upright on a table. Students will observe the settling of the sands. It may take several hours for the glacial till or the Caribbean sand to settle. The Quartz sand will settle first.

Session 3

Students will make a small sedimentary rock sample from sand and a concentrated solution of Epsom salt. Students should pack the sand firmly (deposition) and place it in the paper towel. The samples will need to dry over night. The Epsom salt is a weak binder for the sand particles (cementation). It is only meant to simulate the bond that can occur in sedimentary rocks. The cementation binder in sedimentary rocks can be iron, silica, or lime.

Basic Skills Development:

Observing

Manipulating Materials

Inferring

Describing

Discussing

Evaluation Strategy:

Students will describe how sediments deposit in water and demonstrate how sedimentary rocks form.

Vocabulary:

sedimentary

compaction

sediment

deposition

cementation

Objective: Students will describe the deposition of various types of sands and create a sedimentary rock using sand and Epsom salt mixture.

How are sedimentary rocks formed?

Session 1

5 cc samples of each type of sand should be measured in a medicine cup and placed, one at a time, in a petri dish. Using a double lens magnifier, ask students to observe the characteristics of each type of sand provided. Students should write or draw a description of what the sand looks like on their activity sheet for Learning Experience 4 in the Rocks and Minerals and Landforms Student Activity Book. (Please see PDF) Make sure you keep your medicine cups for Learning Experiences 6, 7 and 9. Make sure you keep your petri dishes for Learning Experience 9.

Discussion Questions:

What are the similarities and differences you see between the three samples?

Are the grains the same size? Shape?

Session 2

Sediments are small solid pieces of material that come from rocks or living things. Water, wind, and ice can carry sediment and deposit it in layers. If water is carrying the sediment, the larger, heavier rock fragments sink to the bottom first. Students can observe this through the following teacher demonstration. Place 150 cc of water in each of the three clear plastic tubes provided in the kit. Place 30 cc of the quartz sand in one tube, 30 cc of Caribbean sand is the second tube, and 30 cc of the glacial till in the third tube. Cap the top of each tube and shake the tubes. Ask students to infer how the sands and the glacial till will settle in the tubes and then observe how the sediments fall back to one end of the tube. Discussion Questions:

What happened to the sediments? (they formed into layers)

Which layer appears to have settled to the bottom first?

Why do you think this occurred?

From this activity, what is one of the most important properties of sedimentary rocks? (layered texture)

Are the grains that you observed angular or rounded? (rounded)

Why do you think so? (grains collide with each other as they are transported in rivers so they eventually become rounded)

Session 3

Once sediment has been deposited, the process of compaction and cementation changes the sediment into sedimentary rock. To simulate this, students are to make three sedimentary rocks with the three types of sands provided. Students are to first create an Epsom salt mixture that is used as the “cement” for the rock. This mixture is made by mixing together with a plastic spoon 20 cc of warm water and 10 cc of Epsom salt in a 2 oz plastic cup. It will take a few minutes for all the Epsom salt to dissolve. Students are to mix 20 cc of the Caribbean sand and 5 cc of the Epsom salt mixture in another 2 oz plastic cup.

Place the sand and Epsom salt mixture into a paper towel that has been folded in half, then folded in quarters to form a pocket. The sand needs to be firmly packed. The paper towel can be stapled shut and hole punched at the top of the paper towel. A paper clip should be placed though the hole and a piece of string tied to the paper clip so it is then able to hang and dry. The sample should be attached to a string with a clothespin. The process must be completed with the quartz sand, glacial till, and the Epsom salt mixture.

Note: The dried sedimentary rock sample will be fragile. Once the “rock” has dried, open the paper towel and observe the sedimentary rock that has been created. Record your observations on the activity sheet for Learning Experience 4 in the Rocks and Minerals and Landforms Student Activity Book. (Please see PDF) Test the strength of each rock. Save one piece of the dried sedimentary rock sample for the hydrochloric acid test.

Compare the sedimentary rocks you have made to the sedimentary rocks in the rock collection.

Discussion Questions:

How do you think the layers of sediment become rock? (the layers are buried within the Earth’s crust. The layers become compacted due to the weight of the layers above it. The water is squeezed out of the layers and the minerals left behind to fill the spaces and act as a cement to bind the grains together.)

How do the sedimentary rocks in our collection compare to the one we made?

What do you see what sedimentary rocks have in common?

Look at the fossil sandstone rock? At what point in the sedimentary rock formation process do you think the fossils were formed?

Folding of a single sheet of paper towel to form a pocket. Pack the sand and Epsom salt mixture firmly.

Session 4

A hydrochloric acid test is another rock identification test. Students are to use the sedimentary rocks they have just created and perform a hydrochloric acid test on them to test for carbonates or limestone. If the rock has calcium carbonate in it, it will have a bubbling and fizzing reaction. Students are to trace their petri dish on a piece of white copy paper. They can then cut out their circle approximately 3 mm. inside the line they drew so the paper circle will fit into the bottom of the petri dish. Students are to break off a piece of each of their sedimentary rocks and place the pieces into their petri dish. Students are to add 2 – 3 drops of hydrochloric acid to each piece of rock and observe the results. Students will notice that the rock made with the Caribbean sand and the glacial till react with the hydrochloric acid while the quartz sand rock does not.

Discussion Questions:

What is your explanation for why some of the rocks made from sand reacted with the hydrochloric acid and some did not?

For the accompanying Rocks, Minerals, and Landforms Student Activity Book, please refer to the PDF found here. (Please see PDF)

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