Question 1. Many hills in California are known to have troubles with landslides when heavy rains soak the area. The clay smectite is frequently found as a major mineral component within the soils of these hills. Smectite is known as a phyllosilicate.

The California Geological Survey analyzed two samples using XRD: one dry soil, and one wet soil. The XRD powder pattern for the dry smectite-rich soil is shown in Fig. 2. Using the Bragg equation (assuming n = 1) and the fact that Cu Kα radiation was used (where λ = 1.541 Å), what is the d-spacing for the (001) peak found at 2θ = 5.82^o?

Question 2. For the wet soil sample, the (001) peak shifts to 2θ = 4.2⁰. Calculate the d-spacing for the wet smectite.

Question 3. What happened to the smectite crystal structure, when it was exposed to water?

Question 4. The shape of the dry smectite (001) diffraction peak (and others) in Figure 2 is not symmetrical: sharp on the low 2θ side and very broad on the high 2θ side. What does the shape indicate about the distribution of the d-spacings associated with that diffraction peak? 

Question 5. How does this structural change in smectite relate to the larger scale structural instability of the landforms when exposed to heavy rain?