ES 4901 Petrology
Homework 5
Name _____________________
This homework is for Chapter 6, which mainly treats Binary Phase Diagrams
1. In the Makaopuhi Lava Lake studied by Wright and Okamura (1977) Olivine
appears first, then decreases as pyroxenes start. Why does it decrease? What
textural evidence do you expect?
2. In a P-T phase diagram, give examples of phases.
3. In a P-T phase diagram plotting the polymorphs of Al2SiO5, name the phases and
component.
4. State the Phase Rule if neither pressure nor temperature is fixed.
5. Define solid solution
6. Explain the lever principle
7. In the cooling system Anorthite – Albite, if no fractionation occurs, the
composition of the last crystals formed is
a. the same as the bulk composition
b. very different from the bulk composition
8. In the cooling system Anorthite – Albite, if fractionation occurs, the composition
of the last crystals formed is
a. the same as the bulk composition
b. more silica rich than the bulk composition
9. In the cooling system Anorthite – Albite, the central field, between the liquidus
and solidus, has
a. one phase
b. two phase
10. Use the two component ( = binary) eutectic system Diopside-Anorthite (NO solid
solution) to explain why, in some rocks pyroxenes crystallize before plagioclases,
contrary to Bowen’s Reaction Series.
11. In the binary eutectic system Diopside-Anorthite (no solid solution), the last
liquid to crystallize is at the eutectic composition d. True or False?
12. In partial melting of the Diopside-Anorthite system above, The melting solid
would be either pure Di or An depending the on bulk composition X. After one
solid is consumed, the temperature would rise, with no further melting occurring
until the melting point of the remaining solid. True or False.
13. In the system Forsterite –Silica, crystals of early forming Olivines (Forsterite) are
removed. This removes Mg++, and the melt shifts to
a. more silica-rich compositions.
b. more silica-poor compositions