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Element Partitioning and Distribution Coefficients
SERC Workshop 2010 Teaching Geochemistry Valerie Reynolds Colby College
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Goals for this activity
Students learn how distribution coefficients are calculated, the conditions that influence partitioning behavior, and how to apply this knowledge when reading primary literature.
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Audience Junior-level undergraduate elective Mineralogy prerequisite
Chemistry is a prerequisite for Mineralogy May have had Petrology Assignment is stand-alone exercise w/out discussion Can be manipulated to suit different manuscript/chemical composition (e.g., granite rather than basalt)
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Higher Order Thinking Skills
Students learn how to read scientific literature with a critical mindset so they can evaluate the merit of the interpretation presented in the paper. Husch (1990)
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Exercise Overview Part I: Cationic Substitution
Mineralogy review Part II: The Distribution Coefficient Explore Kd via GERM Part III: Application of Knowledge Read manuscript that uses chemistry to interpret crystallization sequence
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Part I: Cationic Substitution
Students refresh Mineralogy concepts Factors influencing cationic substitution Coordination #’s of elements in Earth’s crust Predict elemental substitutions Basalt, specifically Given: Ni common trace element in basalt Review basalt mineralogy and element CN’s Predict for what/in what Ni substitutes
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Part II: The Distribution Coefficient
Geochemical Earth Reference Model GERM: ( Provide specific instructions (Ni/olivine/basalt) Range of Kds How determined? Links to references Calculate Kd using mineral/matrix data Compare with predicted results from Part I
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Part III: Application of Knowledge
Use Georef to look up article Husch J.M. (1990) Palisades sill: Origin of the olivine zone by separate magmatic injection rather than gravity settling. Geology 18, Discussion of pyroxene vs olivine accumulation Ni, Cr, and Sc Timing of plagioclase crystallization Husch (1990)
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Part III Cont’d Summary and Discussion
Students assigned in groups of ~3 Groups meet to discuss paper/answer questions Individuals write summaries Class Discussion
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Student Feedback Exercise led well into article material
Guide questions appropriate Article at appropriate level Discussion particularly helpful Subsequent assignments have students develop the guide questions
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