STUDENTS EXPERIMENT WITH “COOKING ROCKS”: APPLICATIONS TO UNDERSTANDING HEMATITE DIAGENESIS ON EARTH AND MARS

Teaching diagenesis (post-depositional origins/change) is important to help students understand the history of sedimentary deposits, lithification, fossil preservation, evolution of mineral and hydrocarbon resources, as well as surface processes on Mars. Interest in Mars diagenesis is now heightened because of NASA rover discoveries of hematite spherules (“blueberries”) and the inference to the existence of water. Non-majors through advanced geoscience students can grasp concepts of mineral stability and diagenesis through a simple cooking experiment.

The basic experiment materials include goethite-cemented sandstone samples, oven access, and a digital camera to document before/after results. Students can evaluate how the formation of iron oxide minerals requires water. In the experiment, goethite (FeOOH) can transform to hematite (Fe₂O₃) by cooking the sandstone in a conventional oven (400+ degrees F) for an hour or more. Safety goggles and insulated gloves/potholders are recommended as a safety precaution. Students utilize the scientific method by outlining their hypothesis, methods/test, results, and conclusion. To document the change in mineralogy, before and after pictures are taken of the sample in the same position with a consistent scale.

To extend exploration, students can investigate: 1) analytical instrumentation (e.g., XRD or Vnir spectroscopy) to identify the before and after sample minerals; 2) additional experiments on whether adding more water after would produce further change; 3) aspects of time and how quickly change can occur; and 4) published literature to understand how Earth analogs and/or experiments helps scientists understand conditions of hematite formation on Mars. This easy recipe “rocks” with students.