Review Questions for Chapter 3: Textures of Igneous Rocks.
1. Other than the externally-imposed cooling rate, what are the three principal rates that govern rock
texture?
2. What is typically the determining (limiting) rate when large crystals form? Explain.
3. What is the determining rate when dendritic crystallization takes place? Explain.
4. What is the distinction between primary textures and secondary textures?
5. Explain how porphyritic texture is most likely to develop.
6. Pyroxene can be replaced by hornblende, biotite, or chlorite as a pluton cools. Hornblende can be
replaced by biotite or chlorite. Biotite can be replaced by chlorite. What common feature of these
sequences most easily explains them? Hint: look up the formulas of each mineral.
7. Quartz commonly exhibits interstitial texture with respect to feldspars. What does this imply in
terms of crystallization sequence? Why?
8. What is “normal” zoning in a plagioclase? Give two reasons why plagioclase typically exhibits
zoning in thin section whereas olivine does not.
9. What is cumulate texture and how does it form?
10. Are vesicles more plentiful in the upper portions or the lower portions of basaltic lava flows? Why?