Mineral Cleavage: a practical experiment
In this geology activity, students investigate the physical property of mineral cleavage by physically trying to break down a block of halite and describing the results. This lab addresses many misunderstandings non-majors have about the physical properties of minerals and includes a brief write up of their conclusions.
Students will learn about:
- mineral cleavage, crystal structure
- repeatability/reproducing scientific results, scientific writing
Context for Use
This project is designed as an in-class project for freshman introductory geology labs. It should take no more than 10-15 minutes, and ideally should be done in a group setting. Required equipment includes eye protection, and a rock hammer. The project is situated in the first lab of the course, as a introduction to rocks and minerals. It should be easy to adapt it to other settings, although more supervision would be advisable for younger students (middle school and younger).
Description and Teaching Materials
Activity description including questions students must answer after performing activity.
Activity description for mineral cleavage activity (Microsoft Word 20kB Jun29 09)
Teaching Notes and Tips
For this activity, students are most often confused in two areas: distinguishing mineral cleavage and fracture, and the preconceived notion that all mineral samples should be perfect. They also often confuse the natural crystal form of a mineral (ex. quartz) and cleavage surfaces. The best way to overcome these confusions is to show good examples of your samples, but emphasize that perfect examples are not usually the norm. Remind students that they will improve with experience, initial confusion is understandable.
Wearing eye protection is essential for this activity. Also remind them that a rock hammer (or whatever implement you are using to break down the halite) is not a toy and should not be aimed at other students or lab equipment.
To emphasize the process of science, remind students that as scientists we do not know what our research may yield, just as they do not know which way the halite will break. We also must address the issue of repeatable results; so they should notice if the mineral breaks in the same general way each time.
Assessment is guided by the students' answers to the questions in the lab activity, with special attention paid to their thought processes, not necessarily the exact correct answer (i.e., recognition of the existence of cleavage is deemed more important than their correct identification of 3 cleavage planes in the specific mineral).
References and Resources