Objectives: This is an introductory exercise that is designed to 1) help students develop their observational, descriptive, and interpretive skills; 2) place classification systems in a rational context based upon the student’s observations; 3) prepare students for more detailed coverage of material by encouraging them to ‘be scientific’; and 4) demonstrate effective teaching practices using a constructionist approach, collaborative learning, and peer assessment.
Assignment: Develop a classification system that will differentiate and organize the materials furnished. Your classification system must have the following:
1) the system must be expandable, so that you can use it to classify new materials that may be discovered;
2) the system must be reproducible, so that other scientists can use your criteria to come to make the same interpretation about classification that you have originally determined;
3) the system must be easily applied by other workers who will need to use it to effectively in the field or in the lab.
Work in small groups(3-4) to develop your classification system. First, look at all the objects as a group. What characteristics do you see(you may have to use your hand lens to see the smaller objects), feel, smell, taste, hear, or whatever that the objects have that could be used to compare and contrast them. For example, some of the objects have different colors. What is color? If you choose color as a defining characteristic, how many choices do you have? Some of the objects have different shapes. Why does any object have a particular shape? If you choose shape as a defining characteristic, how many choices do you have? Some of the objects look like metals whereas others do not. Why? If you choose this as a defining characteristic, how many choices do you have? Some of the objects are magnetic whereas others are not(use magnet in lab kit to test). Why? If you choose magnetism or lack of it as a defining characteristic, how many choices do you have? Make a list of the characteristics you find. Next, you will have to come to a consensus about which properties should have the highest priority, which properties are useful for general discrimination of materials, and which properties may be diagnostic of specific materials. Your final product should be a taxonomic ‘tree’ with a written description of how to systematically use your procedures to classify materials.
Selected groups will present their classification system to the class.
Assessment: Trade your classification system and ‘user’s guide’ with another group. Each group should then assess how effective the classification system is. Pick out a number of representative materials and use the system to see if you get the same answer as the original group. Did you run into difficulties in making decisions about the characteristics of some of the materials? Take a ‘newly discovered material’ (provided by your instructor) and see how this system works for the new material. Is this system internally consistent (i.e., you get the same answer for the same types of materials)? Is it easy to use? Provide constructive advice on problems you may have encountered, and provide some suggestions on how you could solve this problem. This is meant to be an informative review that allows you to help you colleagues better perform their tasks.
This is not an exercise in destructive testing. Many of the materials provided are excellent examples. Keep them that way. When in doubt, ask your laboratory instructor.
Modified from:
Mogk, David W. (1997), Mineral Classification—What’s in a Name? In
Teaching Mineralogy, edited by John B. Brady, David W. Mogk, and Dexter Perkins, Mineralogical Society of America, Washington, D. C., pgs. 37-41.