Teach the Earth > Mineralogy > Teaching Activities > Mineral Recalculation Using Remote Electron Microprobe Analysis

Mineral Recalculation Using Remote Electron Microprobe Analysis

Sven Holbik & Rosemary Hickey-Vargas, Florida International University
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Summary

This in-class activity uses the remote capabilities of the electron microprobe (EM) system with wavelength dispersive spectrometry (WDS) available through the Center for Analytical Electron Microscopy (FCAEM; http://fcaem.fiu.edu) at Florida International University in Miami FL, to introduce students to microprobe analysis, determine the major chemical elements in a mineral, use the chemical data to calculate the exact chemical formula of the mineral and to plot this data on a binary phase diagram for interpretive discussions.
This instructor led activity is intended as a whole-class demonstration of the EM with WDS analysis of minerals. The remote user will navigate the EM stage to find phases of interest, acquire images of phases, set up multiple points for analysis, and disseminate collected data for students to answer questions given in lab assignment.

Context

Audience

This assignment is intended for sophomore or junior level course in Mineralogy or Petrology. The remote use of the electron microprobe can be projected on a projector screen or wall so it can accommodate large classes (~25 students or more).

Skills and concepts that students must have mastered

Students should have some background in electron microscopy including the detection of secondary electrons, backscattered electrons, characteristic x-rays, and the use of wave length dispersive spectrometers. Students must also have been introduced to the olivine binary phase diagram and idealized chemical formulas for olivine (or any mineral of interest used as defined by remote user).

How the activity is situated in the course

This activity serves as an in-class demonstration of electron microprobe via WDS analysis for students in a Mineralogy or Petrology course. This is stand-alone lab that introduces students to electron probe microanalysis and may prepare students for individualized use of the EM for term projects later on in the semester.

Goals

Content/concepts goals for this activity

The objective of this activity is to introduce students to electron microprobe instrumentation and analysis, understand mineral formulas and compositions, use chemical data and formulae to determine acceptable analysis, and familiarize students with phase diagrams and equilibrium crystallization.

Higher order thinking skills goals for this activity

This assignment moves past low-order thinking skills involved in the mechanics of running the electron microprobe and gets students to question the quality of the data acquired and how mineral composition relates to crystallization and magmatic processes.

Other skills goals for this activity

Description and Teaching Materials

Lab Assignment (Microsoft Word 2007 (.docx) 16kB Aug14 15)

EPMA Remote Startup Procedures (Acrobat (PDF) 308kB Aug14 15)

EPMA General Operational Procedures (Acrobat (PDF) 2.1MB Aug14 15)

Teaching Notes and Tips

This EM in-class demonstration using WDS may take between 30 minutes to an hour depending on how many mineral phases are analyzed. This lab is designed for the analysis of olivine and FCAEM has specific basaltic samples containing ample olivine phases, however, remote users can use their own samples using other phases for the demonstration and analysis given that the remote user has shipped samples to the center (please remember to allow time for carbon coating of thin sections). Video tutorials are available for remote use of EM with EDS at fcaem.fiu.edu/tutorials/. Users are encouraged to schedule practice time on the EM with or without FCAEM staff guided help. A practice run through with the EM will give the remote user a good approximation of how long the lab activity will take and the user can even digitize exact locations for analysis prior to demonstration.

Assessment

If the students have correctly answered all questions and provided adequate explanations for mineral composition variability then the goals of the assignment have been met.

References and Resources

Florida Center for Analytical Electron Microscopy
Video tutorials at https://fcaem.fiu.edu/tutorials/
MINDAT.org (data for mineral composition and formulas)
Microprobe description by John Goodge in SERC
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