Igneous Cooling Rates, Crystal Size, and NOT Getting the 'Right' Experimental Results

Thursday 3:20pm-3:40pm Weeks Geo: 140
Teaching Demo


Mary Colson, Moorhead Public Schools
Russ Colson, Minnesota State University-Moorhead


Participants will make observations of real experimental results, watch videos of thymol experiments, and consider the role of the teacher in facilitating argumentation and modeling in the classroom.


The organic compound thymol, with a melting temperature of 48°C, can be used to give students an opportunity to experiment with the effects of cooling rate on crystal size. We examine how a cookbook lab, which was designed to 'confirm textbook information,' can be transformed into an authentic scientific investigation in which students and teacher face unexpected results together. These experimental surprises give opportunity for student-student and teacher-student interactions in which students argue from evidence, develop models for what's happening during crystallization, and revise and redo experiments in response to new understanding.

Attendees will examine typical products of thymol cooling-rate experiments, evaluate how well the experiments support the textbook model, and consider possible causes of discrepancies. We will watch videos of cooling-rate experiments and consider how students and teachers together can develop their own models to explain what's going on. We will examine not only how students become engaged in real science investigation when results are unexpected, but how the teacher as a practitioner of science is a necessary ingredient in mentoring students through thinking about those unexpected results.


This activity is appropriate for 8th grade, high school, or introductory college students and might be particularly appropriate as a college science methods class activity.

Why It Works

Real science investigation rarely provides straightforward answers that simply confirm a preconceived notion. Rather, real science involves observation of puzzling phenomena that require arguing from evidence, model creation and revision, and often new experimental designs to test developing ideas. The activity we propose provides opportunities to consider experimental results that are rarely simple or straightforward but which nevertheless bear on ideas important in reading the stories that rocks tell. It does so while giving students and teacher the chance to work together in a collaborative environment.



Presentation Media

Igenous rocks, crystallization and NOT getting the right answer (PowerPoint 2007 (.pptx) 86.9MB Jul20 16)