Swelling Rocks

In-Class Activity 1_Life Hosting Rocks & Minerals

Julia Kahmann-Robinson PhD and Marjorie Chan PhD, University of Utah Department of Geology & Geophysics

Purpose

Explain why clay soils expand and discern where clays might be present on Mars.

Engage

Observe the class demonstration or video [http://www.youtube.com/watch?v=ACpuYED9WkU] and answer the following questions.

1. According to the demo/video, why is the soil expanding?
2. How is the bulk density changing? What is this change indicating?

Explore

The molecular level- Utilize the diagram to the right to help students understand how clays are made up of stacked layers.

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Figure 1. Diagram of an expandable clay such as montmorillonite or bentonite (Butt et al., 2003).

Provenance: Butt et al., 2003
Reuse: This item is offered under a Creative Commons Attribution-NonCommercial-ShareAlike license http://creativecommons.org/licenses/by-nc-sa/3.0/ You may reuse this item for non-commercial purposes as long as you provide attribution and offer any derivative works under a similar license.

Have students answer the following questions:

1. In Figure 1a, how are the water molecules influencing the structure?
2. Why do you think the water attracts to the clay rather than the sand of the sandy loam (consult Figure 1b)?

Explain

Share the following information about clays with students:

• Clays are expandable due to their layer charge. The higher the layer charge (for example montmorillonite or bentonite) the more the clay will expand.
• The interlayer (the charged layer) attracts water molecules allowing for the clay to expand
• Clays are commonly formed in the pedogenic, hydrothermal, or acid lake environment on Earth.

Elaborate

Given your understanding of clays now, if clays [Na_0.2Ca_0.1Al₂Si₄O₁₀(OH)₂(H₂O)₁₀] are observed on Mars....what does this mean?

Evaluate

Where might you look to find clays on Mars (what kind of features)? Hint: consider their environment of formation, do we have evidence for their presence on Mars?

Watch this video about clay minerals on Mars: http://www.youtube.com/watch?v=cmc54EPvMZE