Geochemistry 428/628
Exam 3 sample questions

Notes:
The final exam will concentrate on material covered since the last exam. It will include basic concepts of geochemical modeling, and will include questions based on your class presentations! A class like this inherently builds on concepts discussed earlier in the semester, so by definition, it is cumulative.

Example Questions

  1. What are delta-D and delta-18O?
  2. Describe and account for the measured delta-D and delta-18O in meteoric water across North America.
  3. Describe a way oxygen isotopes can be used as a paleothermometer.
  4. Why do water and steam in geothermal areas usually display a delta-18O shift, but not a delta-D shift?
  1. Weathering of pyrite-bearing shales in North Dakota might lead to the formation of the sulfate mineral
    potassium jarosite, KFe3(SO4)2(OH)6. Write a balanced equation for the reaction pyrite --> jarosite.
    (Obtain K from the environment).
  1. What is pe, and how is it related to Eh? How is it measured?
  1. Consider the Eh-pH diagram given in Faure, Fig. 21.1a.
  2. Write the chemical reaction between tenorite (CuO) and Cu2+ in terms of water and hydrogen ion.
  3. Derive the Eh-pH equation for this reaction.
  4. What concentration of Cu2+ would be found in a lake having an Eh = 0.40 and pH = 7.5?
  1. In his classic study of the saprolites formed on granitic gneisses in Minnesota, Goldich observed that potassium feldspars weather more slowly than plagioclase feldspars. What could be a reason for such a phenomenon?