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Paper No. 33-10
Presentation Time: 3:55 PM
STRING CHEESE: A PERFECT ANALOGUE FOR PERFECT CLEAVAGE IN TWO DIRECTIONS
String cheese and some minerals exhibit similar rheological behavior due to the nature of the molecules that compose them. Simply put, string cheese exhibits excellent cleavage in two directions. This distinctive characteristic is a result of heating and stretching (or extruding) the cheese such that the protein molecules are aligned with the long axis of the cheese cylinder. Just as in a mineral, the string cheese will tend to cleave along these bonds, rather than across them, when stress is applied. The stringiness of string cheese is used as an analogue to introduce the concept of cleavage in minerals in an introductory level Physical Geology course. The goals of this lesson are (1) for students to be able to explain the relationship between cleavage and the arrangement and strength of bonds within a mineral, (2) to predict what will happen to minerals with various directions of cleavage when stress is applied, and (3) to identify cleavage in a mineral. Students engage in a series of active learning exercises to accomplish these goals. First, students are given string cheese and asked to observe the properties of the cheese, then think-pair-share ideas about why string cheese is stringy and draw a diagram of what string cheese might look like at a molecular scale. Next, students are given pieces of mica and asked to observe the similarities between this mineral and the string cheese. Following discussion, the term “cleavage” is defined using the mica as an example. Finally, students are asked to predict the shapes that would be observed in minerals that have three and four directions of cleavage. The knowledge gained in this lesson is applied during the first stage of a mineral identification exercise, in which students observe hand samples of various minerals and describe the direction and orientation of cleavage planes. Using string cheese as an analogue for cleavage in minerals is a simple and powerful teaching tool that allows students to build upon prior knowledge to construct a meaningful understanding of a complex, abstract concept.