Karl Wirth Macalester College

problem-solving, hypothesis testing, integrating diverse observations and data, relations between rocks and data

databases, sample preparation, instrumentation, spreadsheets, writing, oral presentation

undergraduate majors

introdroductory earth science

This is an example of a semester-long project that integrates many of the aspects of a petrology course

standard tools for teaching petrology (microscopes, computers) as well as some instrumentation (e.g., AA, XRD, XRF, ICP). A comprehensive suite a related rocks that illustrate fundamental petrologic processes is also needed; it is preferred that students can collect the samples in the field.

This approach is time-consuming for the student and the instructor, resulting in less content breadth in the course, but much greater depth.

After completing the course students exhibit greater facility working with large datasets, integrating diverse observations, and improved writing and oral presentation skills. However, this has not been rigorously tested.

The project begins early in the semester when students are provided a suite of rocks, a map, and a lithostratigraphic column from the Sonju Lake Intrusion. Students work as a group to describe and classify the rocks using hand specimens and thin sections. This is followed by detailed petrographic analysis, which provides data about mineral textures, compositions, and proportions. Explanations of the origin and evolution of the intrusion are constructed from the petrographic data and then tested using mineral (SEM-EDS) and whole-rock (XRF) chemical data collected by the students. The explanations of the origin and evolution of the intrusion are further evaluated and revised. Finally, students test their hypotheses using numerical models (MELTS and trace element models) to model their geochemical data. Students present their findings to the rest of the class in oral format and submit written reports.