Jim Rougvie

Beloit College

This is designed for an undergraduate mineralogy class.

Students should be familiar with coordinating polyhedral, coordination number, bonding, substitution and basic mineral properties.

This is a stand-alone exercise that I typically use either early in the course as part of a section on mineral structures and crystal chemistry, or late in the course as part of a systematic mineralogy unit.

The goals are to become familiar with polyhedral models and to understand 1) how the different tetrahedral and octahedral stacking orders in phyllosilicates create different minerals, 2) how chemical bonding is different in these different structures, 3) how the mineral structures and bond types relate to physical properties, 4) how trioctahedral and dioctahedral phyllosilicates are different.

Students synthesize the knowledge they gain to make predictions about physical properties on minerals and reflect upon the advantages of different types of crystal visualization methods.

Students should gain experience in working in groups and sharing their ideas with others, and should gain experience thinking in three dimensions.

In this exercise, students use both polyhedral model kits designed by the University of Wisconsin at Madison Materials Research Science and Engineering Center (MRSEC) Institute for Chemical Education and computer visualization in Jmol to explore the structures of a variety of phyllosilicate minerals, and relate those structures to physical properties. Students work in small groups to build either a sequence of dioctahedral or trioctahedral minerals and answer a series of questions about structure, arrangement, coordination and bonding. The small dioctahedral and trioctahedral groups combine to compare structures and discuss additional questions about these and other minerals.

Students have met the goals if they can correctly answer the questions. This can be assessed by grading a completed assignment, but perhaps is best evaluated by an in class discussion of the answers.

Information about the MRSEC Institute for Chemical Education polyhedral model kits is available here:
http://ice.chem.wisc.edu/Catalog.html

Online interactive instructions on building the structures, including Jmol animations, are available here:
[link http://chemistry.beloit.edu/edetc/pmks/index.html']