PRECIPITATION AND DISSOLUTION OF CALCITE: OCEAN ACIDIFICATION IN A MINERALOGY COURSE (Invited Presentation)

The junior-level course, Mineralogy, starts with hand-samples, then progresses systematically through the mineral crystal systems, integrating mineral identification in hand sample with crystallography, microscope techniques, and phase diagrams. Lecture and lab in week 5 centers around calcite and quartz: hand sample identification; hexagonal crystallography; uniaxial optics; mineral precipitation; the SiO₂ phase diagram; and the chemical potential of aragonite-calcite.

The lab during this week includes the investigation of the precipitation / dissolution of calcite from limewater with addition of CO₂ (from our breath). This will be demonstrated. Students explore the chemistry of the processes, and then extend this to implications for limestone precipitation and carbonate compensation depths. We then connect this demonstration to ocean acidification, the recent and rapid decrease in pH of the Earth's oceans in response to increasing CO₂ in the atmosphere. Students learn of the complexity of the system; that the oceans absorb about one third of CO₂ emissions, slowing effects on the climate, but the carbonic acid produced in the oceans leads to dissolution of calcite. The affect on calcifying organisms and fish are discussed, and the ultimately fate of any animal dependent on sea-life for food.