Relationship between mineral weathering and groundwater composition
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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.
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
More information about assessment tools and techniques.
- 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.
Teaching materials and tips
- Activity Description/Assignment (Microsoft Word 26kB May9 05)
- Excel spreadsheet of published data (Krauskopf and Bird) (Excel 44kB May9 05)
Krauskopf, K.B. and Bird, D.K. 1994. Introduction to Geochemistry, 3rd edition, McGraw-Hill Science/Engineering/Math, 640 p.