Petrographic Problem-Solving Assignments

Jeffrey Templeton
Western Oregon University
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Petrographic problem-solving (PPS) assignments are a series of mini-projects in which students conduct two-week scientific investigations on thin sections and hand samples selected by the instructor. For each PPS assignment, students identify a scientific problem, propose a working hypothesis, collect data to test the hypothesis, and defend their results in oral presentations and written reports. PPS assignments engage students in the study of Earth materials and promote active learning with an emphasis on analysis, synthesis, and evaluation.

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Petrographic problem-solving (PPS) assignments are used in two required upper-division undergraduate courses: a lab-based Petrographic Microscopy course, and an integrated lecture-laboratory Petrology course.

Skills and concepts that students must have mastered

  • Students should know how to operate a petrographic microscope and be familiar with the optical properties that are needed to identify minerals in thin section.
  • Students should have experience identifying basic rock-forming, accessory, and alteration minerals in hand sample and in thin section.
  • Students should have fundamental skills describing and identifying various rock types and textural features in hand sample and in thin section.

How the activity is situated in the course

Students are first introduced to PPS assignments as part of the take-home final in the Petrographic Microscopy course. PPS assignments are continued in the subsequent Petrology course: three are conducted during the 10-week term, and one is completed as a take-home final exam. In Petrology, PPS assignments are aligned with course content and are designed to augment more traditional mineralogy-petrology laboratory exercises (refer to example syllabus provided in supplemental materials section).


Content/concepts goals for this activity

Upon completion of the series of PPS assignments conducted in the Microscopy and Petrology courses, students will be able to:
  • Describe and identify a range of rock-forming minerals, rock types, and textures in both hand sample and thin section.
  • Relate textural features in igneous and metamorphic rocks to their petrogenesis based on direct observations.
  • Apply petrology content and concepts to propose questions of scientific interest and solve geologic problems.

Higher order thinking skills goals for this activity

  • Students gain experience in conducting authentic scientific investigations and are actively engaged in the following methods:
    • Observation
    • Collection and analysis of data
    • Formulation and testing of working hypotheses
    • Synthesis and evaluation
    • Communication of results
  • Students are encouraged to integrate concepts and skills from foundation courses to identify and solve geologic problems.

Other skills goals for this activity

  • Students develop technology skills
    • Acquire digital photomicrographs using microscope and camera interfaced with computer
    • Use software to annotate digital images, prepare multi-media presentations, collect and analyze data
  • Students present results in both written and oral formats for each PPS assignment
    • Write two-page paper for each assignment
    • Present results orally to peers
  • Students defend their interpretations to instructor and peers during oral presentations

Description of the activity/assignment

Petrographic problem-solving (PPS) assignments consist of a series of two-week mini-projects used within the context of an undergraduate petrology course. The central idea behind PPS assignments is for students to use thin sections as a geologic data source for conducting authentic scientific investigations. For each assignment, students are provided a thin section and corresponding hand sample. Drawing from their initial observations and foundation knowledge, students identify a scientific question, propose a working hypothesis to explain it, test the hypothesis using observations and data collected from the sample, and defend their results in oral presentations and written reports. They use digital cameras interfaced with microscopes to acquire photomicrographs and various software applications to collect and analyze data. For each assignment, students prepare a two-page paper and give a brief presentation to the class (5-10 minutes in duration with 3-5 minutes for discussion). During the presentation sessions, which each require a two-hour class period, class members are encouraged to question their student colleagues.

Students are introduced to PPS assignments as part of the take-home final in the prerequisite Microscopy course. Three PPS assignments are in turn engaged in the subsequent Petrology course during the 10-week term. A summative take-home PPS exercise is completed as part of the final exam. In Petrology, PPS assignments augment more traditional laboratory exercises and are specifically aligned with course content, as follows (refer to student handout sheets in supplemental materials section).

  • Using a set of rocks representing distinct lithologies, students are guided to think about what geologic conditions and/or environment the sample formed in.
  • Using a set of plutonic and volcanic rocks from a description and classification exercise, students define their own geologic problem.
  • Using a set of metamorphic rocks, students are instructed to interpret the genetic conditions based on textures and/or mineralogy.
  • Using several different andesite samples, students are directed to consider the origin of the sample in context of a case-study activity conducted during the term. This PPS assignment is completed as part of the final exam and requires a summative two-page paper.

In the context of a broad-based undergraduate Earth Science degree program, PPS assignments engage students in the study of Earth materials, actively involve them in the scientific process, and emphasize creative problem solving rather than factual recall.

Determining whether students have met the goals

To determine whether students have met the learning goals of Petrographic Problem-Solving (PPS) Assignments, the following aspects of student work are evaluated. Because three PPS Assignements are completed in Petrology over ten weeks, students can track their improvement in each area over the course of the term. Grading rubrics are provided in the supplemental materials section below.

Assess quality of geologic problem

  • Does student identify a scientific problem?
  • Is quality of problem consistent with expected performance and background in a required upper-division geology course?

Hypothesis to address problem

  • Does student propose a working hypothesis to address geologic problem?
  • How well does student address specific problem? Is approach consistent with expectations for upper-division Earth Science majors?

Tests of hypothesis and interpretations

  • Does student use data and observations directly available from the thin section and hand sample?
  • Does student support interpretations using textural features and/or mineralogy that are observed in sample?
  • Does student provide relevant data and observations (e.g., mineralogy, modes, textural relations, accurate classification, and use appropriate terminology)?
  • How robust is this data set in addressing problem?

Impressions of paper

  • Writing style and organization
  • Use appropriate figures and/or summary tables to support descriptions


  • Evaluate overall quality, including organization, figures, readable slides, and style during presentation/discussion session

Class Participation

  • Was student engaged in learning process as demonstrated by asking questions of student colleagues?

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