What are THESE rocks (and how did they form)?

Sara Harris and Brett Gilley

University of British Columbia

Undergraduate introductory-level geosciences lab for majors and non-majors.

No prior experience needed.

This is part of a sequence of activities in the first lab of the term.

By the end of this activity, students will be able to:
1. Infer how rocks formed based on observed characteristics.
2. Group rocks into categories based on inferred process of formation.
3. Explain how one rock could be transformed into another rock, for any combination of rocks.

Activity 1: Small groups of students are given 4 rock hand samples per group (granite, conglomerate, sandstone, phyllite). They are told that the four rocks represent the 3 basic categories of rocks, defined by geologists based on processes of formation. Based on their observations, students decide which two rocks formed from similar processes. Students receive no prior instruction, and thus need to use their observations and their current conceptions of how rocks form in order to make and justify their grouping. After small groups have completed their grouping, they report their decision. A full-class discussion ensues, revealing differences among the groups, from which emerge the three rock types and basic processes of formation for sedimentary, igneous, and metamorphic rocks.

Activity 2: Students are given 3 more rocks to put in the appropriate groups, then challenged to draw the rock cycle using their groupings of seven total rocks.

If you only do Activity 1, for assessment, give students additional rocks and ask them to classify them into the appropriate groups. Examples could include: gneiss, basalt, pumice, schist, etc.
If you do both Activity 1 and Activity 2, give students additional pairs of rocks and ask how one could be transformed into the other.