Calculating Compositional Variation and Common Substitutions for Igneous and Metamorphic Minerals
This activity was selected for the On the Cutting Edge Exemplary Teaching Collection
Resources in this top level collection a) must have scored Exemplary or Very Good in all five review categories, and must also rate as “Exemplary” in at least three of the five categories. The five categories included in the peer review process are
- Scientific Accuracy
- Alignment of Learning Goals, Activities, and Assessments
- Pedagogic Effectiveness
- Robustness (usability and dependability of all components)
- Completeness of the ActivitySheet web page
For more information about the peer review process itself, please see http://serc.carleton.edu/NAGTWorkshops/review.html.
This page first made public: Apr 29, 2008
Skills and concepts that students must have mastered
How the activity is situated in the course
Content/concepts goals for this activity
- To apply the principles of crystal chemistry (e.g. Pauling's Rules) to recalculate mineral formulae, and construct structural formulae based on rules of site occupancy;
- To work directly with mineral compositional data, and to critically evaluate the quality of these data by checking mineral formulae for stoichiometry and charge balance; in particular, treatment of ferric/ferrous iron presents difficulties that must be addressed;
- To demonstrate that mineral formulae recalculations are model dependent, and reported values may vary quite dramatically depending on assumptions chosen in selecting recalculation models;
- To become familiar with the compositional constraints of numerous end-members and varieties of the rock-forming minerals that are used to interpret geologic processes, environments of formation, etc., and
- To establish the basis for applying mineral compositions to more advanced applications such as geothermobarometry.
Higher order thinking skills goals for this activity
Other skills goals for this activity
Description of the activity/assignment
Determining whether students have met the goals
Download teaching materials and tips
- Activity Description/Assignment (Microsoft Word 129kB Apr21 09)
- Data Set of Mineral Compositions (Excel 50kB Apr29 08)– Representative feldspar, garnet, pyroxene, amphibole, and mica analytical data from Deer, Howie and Zussman, An Introduction to the Rock Forming Minerals (1967).
Mineral Formulae Recalculation Spread Sheets– these are the spreadsheets used to recalculate mineral formulae in this problem set. Specialized recalculation routines are provided for common rock-forming minerals such as feldspars, olivine, garnets, pyroxenes, amphiboles, micas and epidote. Ferric/ferrous iron ratios can be input if known, or calculated based on stoichiometry and charge balance. Other recalculation procedures are provided based on models of site occupancy of the complex silicate minerals.
See the module on Plotting Mineral Compositions and Chemographic Projections - from Teaching Phase Equilibria.