Do Rocks Absorb Water?

Posted by David Wetzel

Porous Sandstone Rock

Although it is not obvious to the casual observer, rocks absorb water. You can ask your students to observe rocks all day long and they will not be able to tell if the rocks they are observing are absorbing water. However, there is an investigation which allows students to discover that rocks absorb water and how much water specific rocks absorb.

Porous rocks are the best to use for this investigation; however, these rocks are not always available. The best porous rocks are: sandstone, limestone, shale, and granite. If these rocks are not available then a common brick from any home improvement store will work. Bricks are made from same materials found in porous rocks.

Do Rocks Absorb Water Investigation

Materials - per group: large plastic container, large beaker or measuring cup, one brick, water, scale

Procedures -

1. Weigh your brick
2. Place brick in the plastic container
3. Measure the exact amount of water poured into container (ensure brick is completely covered with water)
4. Leave the brick in the container for 30 minutes
5. Remove brick from water and allow all excess water to drain off brick back into container
6. Measure the amount of water remaining in the container
7. Weigh your brick after it has been the water for 30 minutes
8. Ask students questions (see next section)
9. Using the chalk board, overhead, or graphing software projected onto screen create class graph of findings

Ask Students the Following Questions -

1. Did your brick absorb water?
2. What evidence do you have to support your observation?
3. How much water did your brick absorb?
4. What is difference in weight of your brick following the investigation?
5. Additional questioning ideas can be found at 20 Questions to Ask Students in Science Projects

Extension -

1. Allow bricks to soak overnight, then collect data
2. Measure how much water a sandstone rock, limestone rock, and shale rock absorb
3. Students graph the findings using bricks, limestone, sandstone, and shale - labeling dependent and independent variables
4. Ask students which rocks are more or less resistant to weathering.

Resources

Students - Water Science for Schools by US Geological Society

Students - Erosion

Teacher - Understanding Scientific Inquiry

Teacher - Writing in Science