Comparing Quartz Polymorphs

Barb Dutrow (Louisiana State University) and Carol Ormand (SERC at Carleton College)

This activity is part of the On the Cutting Edge Peer Reviewed Teaching Activities collection.

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This page first made public: May 12, 2015

Summary

In this exercise, students compare the structures of low-temperature and high-temperature polymorphs of quartz, relating their differences to symmetry and crystal systems.

Crystallography, Crystal Chemistry, Framework Silicates | College Lower (13-14), College Upper (15-16)

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Learning Goals

After successfully completing this exercise, students will be able to

Make a visual comparison of two similar crystal structures.
Describe key differences between the structures of low-temperature and high-temperature forms of quartz.
Relate atomic structure to symmetry and crystal systems.

Context for Use

Although the apparent focus of this exercise is on the structures of two polymorphs of quartz, it is also about getting students to observe the finer details of crystal structures. It can be used to develop students' attention to detail, whether or not the effect of temperature on the structure of quartz is of particular interest.

Description and Teaching Materials

Students compare the structures of low-temperature and high-temperature polymorphs of quartz in detail, looking at virtual models of the structures from three different perspectives (viewed down each of the crystallographic axes). They are then asked to relate the structural differences to symmetry and crystal systems.

Quartz polymorphs exercise (Microsoft Word 2007 (.docx) 427kB May12 15)

Teaching Notes and Tips

If students have difficulties understanding polyhedral diagrams of minerals, they may find it helpful to complete the Polyhedral Diagrams exercise prior to this one.

Assessment

Student learning is assessed by grading their answers to the questions on the worksheet.

References and Resources

The images in this exercise were created using CrystalMaker software. This software allows students to examine and manipulate virtual 3D crystal structures. It is a great learning tool if your department can afford a site license.

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