Relationship between mineral weathering and groundwater composition

Nancy Hinman
University of Montana
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This activity was selected for the On the Cutting Edge Reviewed Teaching Collection

This activity has received positive reviews in a peer review process involving five review categories. The five categories included in the 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

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This page first made public: May 17, 2005


By observing changes in rocks exposed to chemical weathering, students are to infer resulting changes to the chemical composition of groundwater. Students are required to justify their inferences through the use of chemical reactions involving common minerals. Students must predict outcome of a chemical weathering experiment.

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This exercise is used in an undergraduate course in geochemistry or in hydrochemistry.

Skills and concepts that students must have mastered

  • understanding of major rock-forming minerals
  • understanding of chemical evolution of groundwater
  • understanding of the processes of chemical weathering

How the activity is situated in the course

  • this activity occurs in the first half of the course
  • this activity is an exercise to be conducted in groups
  • this activity is a two-part exercise


Content/concepts goals for this activity

  • Students will need to understand chemical weathering in order to infer changes to groundwater composition.
  • They will need to be able to read histograms and plot data.

Higher order thinking skills goals for this activity

Students are expected to analyze published data in order to develop predictions for how compositions will change in experiments.

Other skills goals for this activity

  • students will work in groups
  • learn to use a pH meter and basic sampling equipment
  • acquire and process data
  • compare observations with predicted results

Description of the activity/assignment

In this pair of activities, students start by using published data to predict what will happen to groundwater composition as a consequence of chemical weathering. The data are provided in a spreadsheet (Hinman_weathering). Students are given the histograms only; both are normalized to 100 %, while one includes silica and the other does not. Students must use resources to predict how groundwater composition will change as a consequence of the observed weathering, and support those predictions using balanced chemical-weathering equations. Afterwards, they conduct a laboratory experiment in which they subject crushed rock to four types of solutions (acid solution, organic-rich solution, rainwater, and alkaline solution). The pH of each solution is measured, and subsequently adjusted after 24 and 48 hours. Solutions are sampled after 14 days. They are analyzed by ICP, and the compositions reported to students for comparison with their predictions.

Determining whether students have met the goals

  • Students are evaluated on the quality and accuracy of their reports on published data.
  • They are evaluated separately on the quality and accuracy of their predictions on the laboratory experiment.

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Supporting references/URLs

Krauskopf, K.B. and Bird, D.K. 1994. Introduction to Geochemistry, 3rd edition, McGraw-Hill Science/Engineering/Math, 640 p.

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