Liane M. Stevens

Bentley College

This assignment is lecture activity/demonstration used with non-science majors in an introductory physical geology course at Bentley, a (primarily) undergraduate business college. The four-credit course meets twice a week; once for a single period used for lecture, and again for a double period used primarily for lab activities. There is no geology major at Bentley; few students elect a broad liberal studies major in "Earth, Environment & Global Sustainability."

Students complete this exercise during the second week of a course on physical geology. Students will have completed a first lab on mineral properties, and so will be familiar with the physical properties of minerals, including fracture, cleavage, and hardness. This class exercise follows a lecture on the rock-forming minerals, which includes introduction to mineral bonds (ionic vs. covalent) and the Si tetrahedron.

Students complete this exercise in class during the second week of a course on physical geology. The exercise follows a lecture on the rock-forming minerals (chemistry, silicates, mineral properties).

The goal of this activity is to develop and reinforce practical understanding of the importance of the silicate structures to the properties of silicate minerals. Content-specific goals include:

1. Students will learn to differentiate (visually and through written description) the differences between five basic silicate structures.
2. Students will study the relationships between fracture/cleavage and bond strength and structure (arrangement).
3. Students will study the relationship between Si:O ratio and structure and will discuss the differences between felsic, mafic, and ultramafic minerals.
4. Students will relate mineral composition (formula) to mineral structure.

Depending on the audience and how the instructor chooses to use this activity, goals for higher-order thinking skills will vary. This activity may be used simply as visual reinforcement for lecture concepts, or may be expanded to include hypothesis-building.

This activity is used to encourage student participation and may be used to encourage group work, presentation skills, and group discussion skills.

Three-dimensional, magnetic representations of SiO tetrahedra and cations are manipulated on a chalkboard to create five basic silicate structures. Students are expected to complete a worksheet accompanying the exercise, which addresses silicate structures, bond types and strengths, physical properties (e.g. fracture, cleavage), Si:O ratio and introduction to vocabulary such as "felsic" and "mafic," and mineral formulae. The worksheet and chalkboard demonstration are designed to simplify silicate structures from complex ball-and-stick models typically used in textbook figures, and to grant students a visual, three-dimensional, manipulable, perspective on what tends to be a confusing concept. This exercise may be simplified or expanded to suit timeframe and the needs of the audience. Benefits of this approach include reinforcement of lecture concepts, broad appeal for a student group with multiple learning styles and degrees of knowledge, and strengthened understanding of the silicate structures.

The activity itself is not evaluated. Students are expected to describe and recognize the five basic silicate structures and to describe the cleavage and Si:O ratio associated with each structure. This knowledge is evaluated during a quiz and/or on a midterm exam.