Interpreting T-X Diagrams

Dexter Perkins

University of North Dakota

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Initial Publication Date: January 18, 2006 | Reviewed: October 18, 2012 (see revision history: 2 events)

Summary

This exercise is designed to help students learn how to interpret T-X phase diagrams. It also introduces them to the systematics of reactions involving a group of minerals.

Metamorphic Processes, Thermodynamics and Phase Equilibria, PTt ...(more) | College Lower (13-14), College Upper (15-16)

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Context

Audience

Introductory Petroolgy

Skills and concepts that students must have mastered

Students must know what mineral reactions are and how to balance them. They should also understand the implications of the phase rule (reactions can only involve a certain number of minerals). They need to know how to add and subtract reactions in order to derive others. Finally, if you expect students to succeed on the very last question, they need to know the basics of Schreinemaker's analysis.

How the activity is situated in the course

This exercise is used near the end of our unit on mineral equilibria. We have already covered the other types of phase diagrams and the phase rule, etc. The exercise serves as an introduction to T-X equilibria. We don't pursue the topic in great depth.

Goals

Content/concepts goals for this activity

The purpose of this exercise is for students to begin to think about T-X phase diagrams and how they are interpreted.
Along the way, students learn that text book authors sometimes make mistakes. The figure in the handout is from Winter's Petrology. But Winter goofed and left some reactions off of the phase diagram.

Higher order thinking skills goals for this activity

The idea is for students to understand the connections between chemical reactions and phase diagrams written on paper, as well as the connections between real rocks and mineral assemblages. The exercise also attempts to establish an abstract-concrete connection.

Other skills goals for this activity

Description of the activity/assignment

This short problem set works well as a group activity that can be completed in class.

The purpose of the exercise is for students to begin to think about T-X phase diagrams and how they are interpreted.

Along the way, students learn that text book authors sometimes make mistakes. The figure in the handout is from Winter's Petrology. But, Winter goofed and left some reactions off of the phase diagram.

Determining whether students have met the goals

The goal is for students to work with their peers and complete the exercise. We then go over their work and discuss any uncertainties that the students may have.

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