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Main Sections

1. Microprobe analyses

2. Mineral groups

3. Solid solutions

Energy of mixing

Mixing on sites

Non-ideal solutions

Reciprocal solutions

Simple models, DQF

Activity calculations

4. Thermobarometers

5. Uncertainties

6. P-T calculations

7. Phase diagrams



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Bulk compositions

Modal proportions

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Practical Aspects of Mineral Thermobarometry

Solid Solutions

This section deals with the thermodynamic treatment of mineral solid solutions, from the practical viewpoint of finding simple but effective expressions for estimating the activities of end members (phase components) to use in P-T calculations. The topic is treated in chapter 7 of Spear's Metamorphic Phase Equilibria. There are several sub-sections:

Energy of mixing, chemical potential, and activity
A brief introduction to the thermodynamics of solid solutions, and the definition of activity.

Mixing on sites
Ionic model, one site, multi-site, end members with part-filled sites (normalisation)

Non-ideal solutions
Simple energetics of non-ideal solutions. Regular and sub-regular models. Multicomponent solutions.

Reciprocal solutions
Interactions between sites

Simplified models, and Darken's quadratic formalism (DQF)
Useful simplified relationships for a-X relations in complex phases

Activity calculations
Recommended models, implemented in Holland's AX program

[ Work is in progress on some of these pages ]

Sources and further reading

This topic is treated quite thoroughly by

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This page last modified 12 October 2004