VISUALIZATION OF FRACTIONAL CRYSTALLIZATION USING A SPREADSHEET PROGRAM

The concept of fractional crystallization as a mechanism of magmatic differentiation is typically introduced in physical geology courses and developed in more detail in petrology courses. This concept can be difficult for some learners to grasp, especially since most commonplace experiences of liquids solidifying, such as water freezing to ice, do not involve multicomponent systems that "freeze" over a range of temperatures. To help students understand what happens to the chemical composition of the residual magma during fractional crystallization, the author developed a spreadsheet program that illustrates these changes with graphical symbols. The program allows one to enter the chemical composition of different igneous rocks in order to visualize how magmas of those compositions would differ from one another. It also enables the user to perform a series of fractional crystallization events (starting with a basaltic magma) to visualize how the residual magma changes in chemical composition as fractionation progresses. Preliminary use of the program indicates that it is useful for some learners. The utility of this approach in teaching fractional crystallization will be assessed more rigorously in a sophomore level course on earth materials.