A Term Research Project Focused on Electron Microprobe Studies of Unknowns in a Junior-Level Mineralogy/Petrology Course

Jeff Ryan, University of South Florida

Summary

As the core activity of petrology portion of a mineralogy/petrology course, students cooperatively conduct petrographic and electron microprobe analytical studies on suites of Central Blue Ridge metamorphic rocks collected during class field activities. We make use of a remotely operable electron microprobe instrument at the Florida Center for Analytical Electron Microscopy (FCAEM) to conduct all analyses in class.

Context

The class (GLY 3311C) targets Juniors. The activity is a term project that begins with a class field trip conducted around midterm. Students have had introductory geology + required Chemistry supporting courses before taking the class.

Audience

The intended audience is undergraduate Geology majors, though we have students from other disciplines (Anthropology/Archaeology, Engineering, Environmental Science) in the course in small numbers.

Class size

15 to 30 students

How the activity is situated in the course

The activity is a half-semester term project that begins with a required class field activity at or near the midterm.

Goals

The first-order learning goals of the activity are to:

• synthesize descriptive and quantitative content covered in the petrology portion of the course (phase equilibria, thermometry/barometry, elemental partitioning), and
• to facilitate intellectual connections between mineral compositions, rock compositions, and mineral associations.

The higher order goals are to:

• get students to evaluate contentions from the geologic literature based on their own observations and measurements;
• gain greater understanding of the strengths and limitations of different kinds of data sources through their own efforts at data collection; and
• synthesize several different kinds of data (petrographic observations, field observations, microprobe mineral chemistry data) in developing a petrologic and geologic history for their field site.

Description

A half-semester term project is used to reinforce instruction in petrology and help students integrate content taught during a mineralogy/petrology course at the University of South Florida.

The project begins with a required field activity, where students collect samples and descriptive field data from several different field sites in the Central Blue Ridge province of the NC Appalachians. Students work in teams on each site, with each student responsible for the preparation of a thin section of one of the rock samples. Students examine their sections petrographically to define mineralogy, and they choose a subset of their samples to conduct further mineral chemistry and textural analysis using the electron microprobe. We use the remotely operable electron microprobe system at the Florida Center for Analytical Electron Microscopy (FCAEM), so students can collect microprobe data during class time, working off computers in the classroom. Students are encouraged to work in teams in their sample preparation and data collection activities, but each student is responsible for writing their own project report, examining relevant background literature, and drawing their own conclusions about the origins and history of the rocks in their suite, based on their team's compiled petrographic, field and microprobe data.

Traditional petrology laboratory activities (thin section studies of key rock types; exercises on phase equilibria, normative calculations for rocks, and thermometry and barometry in metamorphic rocks,) are presented to students as tools they will ultimately use to examine their own samples. I include a whole-class activity focused on introducing electron microprobe analysis to the students in which we run the instrument live in class both to present its various imaging and analysis functions, and to give students some experience in the specifics of its operation (see the An In-Class Demonstration and Activity Using the FCAEM Remotely Operable Electron Microprobe activity sheet for a description of this exercise).

Notes, Tips, and Logistical Considerations

It is important to do some setup on the microprobe ahead of the in-class activity and any student measurements – in particular, one needs to make current measurements on the relevant microprobe standard materials, and establish a standards protocol for student wavelength dispersive X-ray spectrometer (WDS) microprobe measurements. For the metamorphic rock samples we focus on in my class, I generally run a relatively large menu of mineral standards so that we can optimize standardizations and I can give the students some experience in WDS standard selections without the delays involved in running and doing quality control on mineral standard measurements. Often enough the FCAEM technical staff are willing to do standard runs for me overnight, so I don't have to spend a day on it myself.

Generally it is good practice to schedule FCAEM microprobe time several weeks ahead, especially near the end of the Fall semester, when there may be competition from researchers working toward professional meeting presentations.

Costs for remote microprobe usage are listed on the FCAEM website, but can be negotiated for short in-class presentations and the like.

Assessment

Evaluation of the term projects is by way of a rubric, which is handed out to the students. Generally, the sampling sites chosen are not sites where I have done extensive previous work, and I let students know this, noting that there are no "right" answers, and that they are responsible for making and supporting their arguments regarding the origins and history of their studied rock units.

Teaching Materials

• Natural Science Honors “Rocks” Project assignment (Microsoft Word 28kB Nov3 11)
• Natural Science Honors “Rocks” Project rubric (Microsoft Word 30kB Nov3 11)

References & Other Sources of Information

An In-Class Demonstration and Activity Using the FCAEM Remotely Operable Electron Microprobe activity sheet - A description of the in class microprobe operation exercise and a "script" I use in doing it.

Using Remote Microbeam instrumentation in the Classroom: an Experiment - A presentation from the 2010 Teaching Geochemistry in the 21st Century workshop outlining the instructional approach and discussing this class and project.