Teach the Earth > Petrology > Teaching Activities > Introduction to Ternary Phase Diagrams

Introduction to Ternary Phase Diagrams

Dexter Perkins
Univ. N. Dakota
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This activity was selected for the On the Cutting Edge Reviewed Teaching Collection

This activity has received positive reviews in a peer review process involving five review categories. The five categories included in the process are

  • Scientific Accuracy
  • Alignment of Learning Goals, Activities, and Assessments
  • Pedagogic Effectiveness
  • Robustness (usability and dependability of all components)
  • Completeness of the ActivitySheet web page

For more information about the peer review process itself, please see http://serc.carleton.edu/NAGTWorkshops/review.html.

This page first made public: Oct 3, 2011


Includes a number of hands-on exercises involving ternary phase diagrams. Some questions are quite easy, some are not.

Used this activity? Share your experiences and modifications



I use this in my petrology class – mostly juniors.

Skills and concepts that students must have mastered

They should have taken mineralogy and learned all the basics there. Additionally, it helps if they have already discussed igneous rock classification.

How the activity is situated in the course

I use this as an in-class group exercise. Originally I intended that they could all do it without instruction from me and without my help. This does not work for most of my students. So, now I work through a few examples (quickly) before they start. A very important key is for them to read about triangular diagrams before they come to class. Few of my students do that even if I tell them to.


Content/concepts goals for this activity

The goal is or them to understand how to use and interpret triangular diagrams. There is nothing terribly sophisticated about this, but the exercise can be challenging for some.

Higher order thinking skills goals for this activity

This is not all low-level stuff. Some thinking and reasoning is required. And some of the questions involve extrapolation and application.

Other skills goals for this activity

Some students have a hard time translating from abstract diagrams – such as phase diagrams – to real meaning.

Description of the activity/assignment

This exercise is intended as a group exercise to help students learn the fundamentals of using ternary phase diagrams. It is a much better way for students to learn about the diagrams than to lecture to them. Good students will be able to walk through this with little assistance from the instructor.Weaker students will struggle and need help from peers or instructors. The entire exercise takes 1-2 hours for most.

Determining whether students have met the goals

All questions have correct answers, so scoring is easy. If they get all the questions correct, the goals have been met.

More information about assessment tools and techniques.

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