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Construction of Crystal Models and Their Graphic Equivalents

Francis
,
Old Dominion University
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Summary

This laboratory exercise involves construction of physical and computer models of crystals based on a description of their symmetry. The purpose of the exercise is to help you visualize symmetry in two and three dimensions, and to help you explore the relationships between the different crystal systems. It is a problem-solving exercise: the morphology of the crystal is described in simple terms, and both physical and computer models should meet the requirements of these descriptions. Because the physical models may be used in other laboratory exercises, they should be large enough and precise enough for measurement, and durable enough to take handling.

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Context

Audience

This activity is designed for an undergraduate required course in mineralogy and is generally for sophomore or junior level students.

Skills and concepts that students must have mastered

The background students require to complete this exercise includes an introduction to symmetry and to the crystal systems. If the fourth activity is assigned, introduction to Miller indicies, forms and stereographic projection is also needed. I have not tried this exercise exclusively as a "discovery" exercise in which students have no prior introduction to symmetry and crystal systems, although I think this approach might also be possible.

How the activity is situated in the course

This activity is a stand-alone exercise, but is part of a larger volume of classroom and laboratory activities from "Teaching Mineralogy," a workbook published by the Mineralogical Society of America, Brady, J., Mogk, D. W., and Perkins, D., (editors), 1997,406 pp.

Goals

Content/concepts goals for this activity

This laboratory exercise is designed to achieve three objectives:
  1. to fix in students' minds the essential symmetry content of the six crystal systems;
  2. to help students visualize the relation between three-dimensional objects and their two-dimensional representations; and
  3. to help students understand the relationships between the six crystal systems.
Students should see that lower symmetry objects can be visualized as distortions of higher symmetry objects; this is particularly obvious among the crystals with six faces.

Higher order thinking skills goals for this activity

This activity helps students to develop computer models of crystallographic data.

Other skills goals for this activity

This activity aids in student collaboration and group work.

Description of the activity/assignment

This laboratory exercise involves construction of physical and computer models of crystals based on a description of their symmetry. The purpose of the exercise is to help you visualize symmetry in two and three dimensions, and to help you explore the relationships between the different crystal systems. It is a problem-solving exercise: the morphology of the crystal is described in simple terms, and both physical and computer models should meet the requirements of these descriptions. Because the physical models may be used in other laboratory exercises, they should be large enough and precise enough for measurement, and durable enough to take handling.

Determining whether students have met the goals

Each group will be assigned a grade for models and graphics. This group grade will be 50% of the grade for the exercise. Grades for the essay will be the other 50% of the grade.

More information about assessment tools and techniques.

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Other Materials

Supporting references/URLs

Brady, J., Mogk, D. W., and Perkins, D., (editors), 1997, Teaching Mineralogy, a workbook published by the Mineralogical Society of America, 406 pp.

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