EUHEDRA: A PROGRAM FOR TEACHING SYMMETRY IN MINERALOGY (AND MUCH MORE)

Common exercises for learning symmetry in crystals involve the use of crystal shape models. Historically, this goes back to the time of René Just Haüy and his contemporaries. Commonly carved from wood or cast in metal or ceramic, the tactile use of crystal shape models allows one to find symmetry elements simply by inspection. Online instruction makes access to and use of physical models difficult, but 3D computer renderings can be effective alternatives.

There are numerous programs available for rendering and manipulating crystal shapes. However, using such programs to generate models requires much of the basic knowledge that instructors are often trying to teach. It is very useful to have a set of premade crystal shape models that can be simply used for rotating in space to look for the presence of symmetry elements. In addition, there are other desirable properties of such a resource that would make it most effective for teaching. For example, making certain properties of a model such as the point group symmetry unavailable to students is desirable. This would help prevent easy circumvention of having to find the symmetry in the model by inspection.

Written by Bill Tislar, of T&T Technology, Euhedra is a program for creating and manipulating crystal shape models. A lite version, also available, can open and manipulate premade crystal models but will not allow access to the information used to create those models (e.g. symmetry, Miller indices of forms, etc.). Thus, students can use Euhedra Lite to view and manipulate crystals, similar to having wooden models in hand, but without access to the information that they may be asked to find by inspecting these models.

We have created a library of crystal shape models for use in Euhedra Lite (as well as Euhedra Standard). These include crystal models from all crystal systems with individual forms and form combinations. Euhedra Standard, Euhedra Lite (both versions for PC and Mac computers) and the library of crystal models can be accessed through the Mineralogical Society of America’s Teaching Mineralogy and Petrology Online website: http://www.minsocam.org/msa/Teaching_Resources.html