Answers for Chapter 24: Stable Mineral Assemblages in Metamorphic Rocks 1.What is meant my mineral paragenesis? 2.Goldschmidt’s mineralogical phase rule is φ= C. Why should this be true for a typical metamorphic rock? 3.What are the implications for a metamorphic rock in which φ< C? 4.One alternative explanation for a metamorphic rock in which φ> Cis that equilibrium was not attained. Explain why disequilibrium would tend to raise φ. 5. Another alternative explanation for a metamorphic rock in which φ > C is that the sample was collected exactly on an isograd. Explain how this might be possible. If a sample is collected on an isograd, both the reactants and products of the isograd reaction will be present. That means more phases than would occur between isograds where only the stable products are present. 1
6. A “perfectly mobile” component is one for which the chemical activity is controlled externally to the system, whereas the activity of other components is controlled within the system. As a slight simplification, let’s treat activity as though it were composition . Consider a system of your own creation in which a saline NaCl solution acts as a pore fluid able to flow through a porous container of sand-sized grains of quartz and halite. Devise a simple system in which Na + and Cl - would be considered perfectly mobile (concentrations controlled externally) and another in which they would not (concentrations controlled internally). Describe the two systems (using the mineralogical phase rule), both before the fluid is added and after equilibrium is attained.
- Fall '09
- Metamorphic rocks, phase rule, GRT, mineralogical phase rule