Jeff Ryan

University of South Florida, Department of Geology

A Junior or Senior level course in Petrology, or a senior/first year graduate course in Geochemistry. It can also be part of a graduate level course in Analytical Methods.

To get the best benefit from the activity, students should have had experience translating oxide weight percent data for minerals into mineral formulas, and they should have enough background in the mineral assemblages and phase relations of igneous or metamorphic rocks to be able to try and predict the occurrence of other minerals in an assemblage based on the recognition of key phases. Having had some past experience with X-ray diffractometry, so as to understand the nature of X rays and the processes of diffraction and fluorescence is very helpful.

I use this activity as the class introduction to the use of an electron microprobe to conduct mineral chemistry analyses, which they will do as part of group term projects later in the course.

The intent of this activity is help get students over the relatively substantive hurdle of learning the operation of a complex piece of analytical equipment. As such, it is an introduction to the theory of electron microprobe analysis, and a demonstration of its routine use.

This activity is actually aimed at quickly getting past the lower-order thinking skills involved in learning the mechanics of use for a complicated analytical instrument.

Normally learning to use instrumentation happens individually or with small groups of students, and it is highly time-inefficient. This exercise is aimed at trying to get past a common perceptual obstacle with instrument use: student confusion associated with multi-step procedures for instrument operation, and associated fear of making a mistake that might do harm to the instrument.

The ability to make real analytical use of research instrumentation in the classroom via remote operation technologies has the potential to both facilitate instruction and support the intellectual transition of undergraduate geoscience students from passive learner to investigator. However, training students in the use of complex analytical instrumentation is a significant time-sink and potential distraction from learning geoscience content.

We make use of electron microprobe analysis as part of a term project in my Mineralogy/Petrology course on the petrogenesis of metamorphic rocks from the southern Appalachians. To try and get past the instrument-training obstacle, I conduct an extended whole-class activity, running the microprobe live in front of the students to introduce the instrument, its tools and functions, and its quirks and limitations. Beyond a simple demonstration I also have the students direct me in the operation of the microprobe to analyze and identify minerals in an unknown sample, to show them how the instrument is used to investigate a sample, and where the hang-ups and easy mistakes are in trying to conduct EDS or WDS analyses. This attempt at a "group training" activity aims to make students more comfortable when they get the opportunity to run the instrument themselves to collect mineral chemistry data on samples they have collected.

The attached documents: a "script" for using the remotely operable FIU-FCAEM electron microprobe in a whole class demonstration and interactive session, along with a simple exercise for translating microprobe data to mineral formulas,

The proof of success in this exercise is whether or not they sit down in front of the computer to run the microprobe and start trying to do things without heavy prompting from me. Also, if they quickly set up to calculate their mineral formulas when their first data starts feeding off the instrument, then the lab time spent on this was not wasted.

• MINDAT.org (data for mineral composition and formulas)
• Microprobe description by John Goodge in SERC