mid-level mineralogy course

This activity assumes students are familiar with the concepts of coordination number, chemical bonding, and basic symmetry. It may be necessary for you to provide a demonstration to the class, including a brief tutorial for using the software available to the students. We recommend XtalDraw or CrystalMaker if you have PC's, or CrystalMaker if you have Macs. You may also want to point out one or more of the following relationships that can be seen in a given model: show how to rotate the crystal in different orientations, identify the location of close packed layers of oxygen, point out similarities among crystallographically-equivalent sites, note the presence of voids in the structure, and demonstrate and explain the benefits and limitations for employing the various rendering options provided by the visualization software (i.e., polygonal, ball-and-stick, and space-filling).

This activity could supplement or take the place of class lectures on Pauling's Rules. This exercise could be run as a lab activity during a single lab session, or split up as smaller modules administered throughout the course to accompany lectures introducing the various mineral groups. Alternatively, this exercise could be assigned as homework for the students to complete at their own pace.

Students will understand various aspects of mineral crystal structures, including: coordination polyhedra, element occupancies in various crystallographic sites, symmetry operations within crystal structures, polymerization of silica tetrahedra, and relationships between crystal structure and physical properties.

This exercise requires students to apply the abstract concepts of symmetry and coordination to actual crystal structures. Spatial thinking skills are also used to visualize the three-dimensionality of the crystal models with the computer (3-D glasses can be used with CrystalMaker to facilitate spatial learning). At the conclusion of the exercise, the students are required to synthesize their specific observations into a set of general principles governing crystal structures (i.e., Pauling's Rules).

Using crystallographic visualization software (CrystalMaker or XtalDraw)

This contribution is modified from a published exercise "Directed Discovery of Crystal Structures Using Ball-and-Stick Models" [Mogk, 1997] . While the published exercise is based on student exploration of traditional ball-and-stick models of crystal structures, this modified version uses a similar "discovery-based" approach and the latest online crystallographic information and visualization software to teach the spatial relationships and crystal-chemical rules that govern the crystal structures of common minerals and crystalline solids. A few changes in the content have been made from the published exercise, mainly to accommodate the new digital media.

The exercise is formatted as a self-paced exercise where students can check their own answers by clicking on "Show answer" tabs. The exercise could be reformatted as a normal homework assignment without the answers given. If used as an evaluative instrument, outcomes could be any of the following: written short answers to the questions, longer integrative writing assignments, or verbal articulation of answers to peers or instructors.