Wendy J. Harrison and Richard F. Wendlandt

Colorado School of Mines

This exercise is used in a sophomore or junior level required course in petrology.

Students should have an understanding of basic physical geology, mineralogy, petrology, and XRD.

This activity is a 2-week project.

This problem develops skills in X-ray diffraction analysis as applied to clay mineralogy, reinforces leacture material on the geochemistry of weathering, and demonstrates the role of petrologic characterization in site engineering.

This activity involves analyzing data.

This activity involves writing and the operation of analytical equipment.

The identification of clay mineral assemblages in soils provides a unique opportunity to demonstrate how basic principles of petrology and geochemistry are applied to engineering design criteria in construction site preparation. Specifically, the problem investigates the conditions leading to the formation of smectite in soils and the resulting construction risk due to soil expansion. Students examine soils developed on igneous, metamorphic, and sedimentary rocks near Denver, Colorado. The field locations are areas of suburban growth and several have expansive soil problems. The 2-week exercise includes sample collection, description, and preparation, determining clay mineralogy by XRD, and measurement of Atterberg Plasticity Indices. This problem develops skills in X-ray diffraction analysis as applied to clay mineralogy, reinforces leacture material on the geochemistry of weathering, and demonstrates the role of petrologic characterization in site engineering.

Students have met the goals of this exercise if they are able to complete the writing assignment and project accurately and completely.