SIMULATION OF MAGMA COOLING USING LOW-MELT BINARY ALLOYS IN GEOLOGY LABS TO INCREASE STUDENT CRITICAL THINKING IN BEGINNING GEOLOGY COURSES

Undergraduate introductory geology classrooms using a traditional lecture format tend to lean heavily on rock and mineral identification lab experiments throughout the majority of the semester. While these lab sessions are a fundamental part of any student’s geology education, the implementation of a student-driven igneous rock crystallization analogue can compliment lesson plans and add variety into the existing standard curriculum of identification labs. With the design of an affordable experiment suitable for undergraduate geology courses that are more advanced and chemistry-related compared to traditional mineral identification, the focus will shift towards experimental labs rather than observational. This allows students to become critical thinkers who are able to utilize and practice the scientific method, which is difficult to achieve using only mineral identification.

Using a 70:30 composition of bismuth:tin as an analogue to magmas and lavas, samples were heated over an open flame until the alloy is melted then cooled on a hot plate from 420°C to room temperature at varying rates to simulate the processes occurring as magma cools into an intrusive igneous rock. The low melting points of bismuth and tin and the simplicity of its binary phase diagram allows for student experimentation to be executed at temperatures achievable in undergraduate laboratory classrooms, particularly in ‘flipped-classrooms’ where class time is used for relevant engaging activities rather than lecture.

The results of the samples supported how the processes of magma cooling at different rates may affect the overall crystal structure of a rock specimen. Some of the samples in which the ramp down from 420°C to room temperature was slower formed larger crystals of bismuth when compared to samples that had a significant increase in ramp down speed, such as flash frozen samples or samples cooled using only ambient room temperature. Interestingly enough, some of the samples formed odd structures where the tin and bismuth settle within the final solid form, along with varying crystal sizes.