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Working with Earth Materials

Many students come into introductory geoscience classes with the assumption that ALL labs in the course will involve rocks and minerals (earth materials). Whether or not this is true for your course, you probably WILL offer at least a few labs where they work with rocks and minerals in some ways. In developing these labs, here are a few questions to consider:

  • What will students need to know for later labs and projects in the course? (e.g. if you plan some kind of mapping exercise, it would probably be helpful to precede that or mix into that a lab where students work with the kinds of rocks they will see later). See the Doing petrology in the gravel pit, Developing a Local Stratigraphy and Geology in a Cemetery examples from the Starting Point field lab module and Geologic Mapping in a Classroom example from the Indoor Labs module as possible models.
  • What does the average citizen need to know about rocks and minerals? (Remembering that most of your students probably enroll in "Terminal Geoscience" when they sign up for "Introductory Geoscience"). Clearly, this question will be answered differently by different instructors. We would argue, though, that the average citizen does not need to know how to recognize and name 50 different minerals and an equivalent number of rocks.
  • What mineral and rock names will you be using in the course that students could benefit from learning about during lab periods? For instance, if you plan to teach Bowen's reaction series in conjunction with a section on igneous processes, it might be helpful for students to work with the eight minerals that are named on the series (and the different igneous rocks dominated by these minerals). Some rock types may be discussed in lectures on composition of the interior of the earth (e.g. peridotite) or biological and geochemical processes on the surface of the earth (e.g. calcite).
  • What do introductory geology students need to know about earth materials if they plan to take more geology courses? (In most introductory geoscience courses, only a minority of students will take more geoscience). The answer to this question may depend on how heirarchical the geoscience department curriculum is and what the obvious second geoscience course will be. It may also be helpful in your course and lab design to consider the conditions that help students transfer content and skills between courses. How People Learn has a good introductory chapter and reference material on transfer of learning.
  • What do introductory geoscience students need to know about earth materials in order to show that they've taken a geoscience course? You may find it a useful learning goal, for instance, for students to learn to distinguish igneous, sedimentary and metamorphic rocks and to explain (using texture and mineralogy) why they assigned a particular rock to a particular category. A lab built on this learning objective will probably look different from a lab built around the learning goal of learning the igneous rock types that characterize each kind of igneous/plate tectonic province.
  • What will students retain? This question is related to the one that involves tranferring knowledge from introductory geoscience to second-level courses and beyond.

Finding sources for mineral and rock specimens

Several commercial companies offer rock and mineral specimens for sale, as complete collections of small specimens, or as single specimens. We find that the smaller (and less expensive) "student specimens" (including those in the "collections") are too small to show important features (like foliation in metamorphic rocks). They are also more likely to disappear. We've found it useful to order several of the "hand specimen" size (generally 2" x 3" to 3" x 4")and then cut each one in half with a rock saw to make up sample sets for student groups of three or four to work on together. (And you can easily cut a thin-section chip at the same time). You can expect to pay more for, say, four hand specimens (to serve eight groups of three in a 24-student lab) than for student-sized specimens for each student.

If you want rock or mineral specimens with certain features (for example, clear cleavage planes in a pyroxend specimen), you'll probably want to work with the company representative to look over some trial specimens. The representative will also be a good source of information about the provenance of the rocks and minerals, information that's unlikely to be very detailed in either print or web catalogs.

In another approach, you can also develop a working rock and mineral collection for introductory geoscience by collecting materials that crop out near your area. North of the glacial margin, you are likely to find glacially transported boulders of igneous and metamorphic rocks that can easily be broken or cut into enough pieces to form a good collection. Some departments send faculty and students on summer excursions specifically to collect rocks for a department teaching collection.

A set of rocks can also be collected and prepared that will tie into a lab reconstructing the geologic history of a particular region (e.g. the Grand Canyon or the Black Hills). These "suites" help students combine rock description with analysis of topographic and geologic maps.

Many student geology clubs at colleges and universities sell rocks and minerals as fundraisers. Western Illinois University, and University of Missouri, Columbia are two examples. Rock sets may also be available through state geological surveys or geological societies, for instance, the Connecticut Geological and Natural History Survey.