Igneous rocks questions

Directions: Use the rock samples, the rock descriptions, and the diagram of the Earth's surface to answer the questions below.

  1. How are the rocks that cooled slowly underground (gabbro, diorite, and granite) similar?  

  2. How are they different?  

  3. How are the rocks that cooled at the surface (basalt, andesite, and rhyolite) similar?  

  4. How are they different?  

  5. Obsidian is volcanic glass. It doesn't have any minerals in it even though it contains all the elements that make up minerals. How is this possible?  

  6. What cooled faster, granite or rhyolite?  

  7. What cooled more slowly, basalt or gabbro?  

  8. What can you learn about the cooling history of an igneous rock based on the size of its crystals?  

  9. A rock with a porphyritic texture has large crystals "floating" in small crystals. Describe the cooling history of such a rock.  

  10. Why do you think that the continental crust "floats" higher on the Earth's surface than the oceanic crust? (HINT: think about how some minerals are heavier than others)  

  11. What national park in the middle of the United States has volcanoes that in the recent past produced pumice, rhyolite, and obsidian? (HINT: it also has famous hot springs and geysers)