Activity 4.1 - Review of Sedimentary Processes
Upon completion of this segment, students should be able to:
- Describe the processes that act to make sedimentary rocks, specifically mechanical weathering, chemical weathering, and erosion.
Context for Use
Description and Teaching Materials
Students often have a hard time grasping the concept of weathering, even with the simple examples that they see every day (such as dissolution and oxidation, a.k.a. rust). This activity will allow students to think about weathering and erosion, and also consider how humans (due to mining activities) increase weathering and erosion rates.
Chemical weathering affects minerals differently. This activity addresses this by showing a drawing of a hypothetical rock on Earth's surface and the underlying sediment. That hypothetical rock contains two minerals, one stable (it resists weathering) and one that dissolves. The soluble (unstable) mineral in the example doesn't completely dissolve but rather one element is extracted. This is similar to the alteration of ilmenite in the Mining Sand activity; iron is removed from the mineral by chemical weathering, leaving a more titanium-rich mineral behind.
It helps to review this drawing (found in the Unit 4 background reading and on this page) in class. Then, ask students to imagine a Peanut M&M.
- What will happen if you put some water on the Peanut M&M? Answer: The color will wash off.
- What will happen to the remaining M&M? Answer: The sugar coating will eventually dissolve but not the peanut.
The Peanut M&M is similar to the rock in the example. The color part of the sugar coating is like the red element in the purple mineral. The peanut is like the grey mineral.
Additionally, you can point out that mechanically weathering often accelerates chemical weathering. For example, if you chew the M&M, then the candy-coating will dissolve faster.
When humans extract mineral resources, they increase weathering and erosion rates. Given that students learned about mining in the previous unit (Unit 3), they can be asked to link mining and weathering/erosion. This can be done verbally with the entire class. Instructors should stress that this is a review/application of concepts from the reading assignment.
- What do we call it when mining companies blast apart the rock to get to a mineral resource? Answer: Mechanical weathering.
- What will happen to the rate of chemical weathering in a place that has been mined, with waste rock either in piles or filling the mine site? Answer: Chemical weathering will occur at a faster rate.
- What is a consequence of this higher chemical weathering rate?
- Large trucks are filled with gravel at a quarry and then carry this gravel to build a road on the other side of town. This is an example of ____________ Answer: Erosion.
Note: The questions in Part 2 can be presented as multiple choice questions and used with clickers.
Teaching Notes and Tips
- Instructor may need to spend additional time with this review and activity if students have not completed the Unit 4 background reading.