Engineering Geology - Chapter 3 - Igneous Rocks

  1. What categories can Igneous rocks be divided into based on minerology
    • Mafic: abundant dark-colored ferromagnesian minerals (e.g., gabbro, basalt).
    • Intermediate: contain roughly equal amounts of dark and light colored minerals (e.g., diorite, andesite)
    • Felsic: contain abundant light-colored minerals (e.g., granite, rhyolite).
  2. How would you distinguish, on the basis of minerals present, between granite, gabbro, and diorite?
    • Granite would have more SiO2 (silica, quartz) than Gabbro. Granite is felsic and lighter colored - more white and pinkish. 
    • Gabbro would have more ferromagnesian minerals than Granite. Gabbro is mafic and darker colored - may be greenish.
    • Diorite would have roughly equal amounts of these minerals. Diorite is intermediate and is black and white looking, like salt and pepper,
  3. List at least 1 rock that you identified in the lab that is a mafic igneous rock.
    • Possible Answers:
    • gabbro; 
    • basalt; 
    • peridotite.
  4. List at least 1 rock that you identified in the lab that is a felsic igneous rock.
    • Possible Answers:
    • granite;
    • rhyolite.
  5. What are the two main ways in which igneous rocks are classified?
    • -Texture 
    • -Minerology 
  6. Name the different possible textures of Igneous rocks, in order from smallest grain size to largest.
    • -Glassy (no grains)
    • -Aphanitic/Fine grained 
    • -Porphyritic (two distinct grain sizes)
    • -Phaneritic/Course grained
    • -Pegmatitic (extremely course grained)
  7. Sort these ingneous rocks, first by texture, then by minerology. 
    -Diorite, Basalt, Gabbro, Granite, Rhyolite, Andesite, Obsidian, Peridotite,
    • Glassy Texture:
    • Mafic: Obsidian

    • Aphanitic/Fine Grained:
    • Felsic: Rhyolite
    • Intermediate: Andesite
    • Mafic: Basalt

    • Phaneritic/Course Grained:
    • Felsic: Granite
    • Intermediate: Diorite
    • Mafic: Gabbro, Peridotite (peridotite can also be listed as ultramafic)
  8. What is the difference between a dike and a sill?
    A dike is an intrusive body that cuts across the layers in the country rock. A sill is an intrusive body that layered in with the layers in the country rock (parallel).
  9. The major difference between intrusive igneous rocks and extrusive igneous rocks is:

    A. where they solidify
  10. Which is not an intrusive igneous rock?

    A. Andesite
  11. By definition, stocks differ from batholiths in
    a. Size
    b. Shape
    c. Chemical composition
    d. All of the preceding
    a. Size 
  12. What is the difference between instrusive and extrusive igneous rock?
    • Extrusive igneous rocks cool quickly at or near Earth’s surface and are typically fine grained.
    • Instrusive igneous rocks cool slowly deep beneath Earth’s surface and are typically coarse-grained.
  13. The most common igneous rock of the continents is
    a. Basalt
    b. Granite
    c. Rhyolite
    d. Diorite
    b. Granite
  14. List at least 2 rocks that you identified in the lab that are extrusive igneous rocks.
    • Possible Answers:
    • rhyolite;
    • andesite;
    • basalt;
    • obsidian;
    • pumice;
    • etc.
  15. List at least 2 rocks that you identified in the lab that are intrusive igneous rocks.
    • Possible Answers:
    • granite; 
    • diorite; 
    • gabbro; 
    • peridotite
  16. How would you distinguish andesite from a diorite?
    Based on grain size. Andesite is a fine grained (intermediate) rock, while Diorite is a coarse grained rock
  17. What grain size is used to distinguish between course-grained and fine-grained igneous rock?
    1mm. Course-grained rocks have grains greater than 1mm, and fine-grained rocks have grains equal to or less than 1mm. 
  18. List a least 2 physical distinctive characteristics of the igneous rock Pumice.
    • Possible Answers:
    •  fibrous;
    • light colored;
    • porous;
    • lightweight
  19. List a least 2 physical distinctive characteristics of the igneous rock Obsidian.
    • Possible Answers:
    • glassy;
    • black,
    • massive (non-porous)
  20. Define Geothermal Gradient. What is the average geothermal graidient of Earth's crust?
    • Geothermal gradient is the rate at which temperature increases with increasing depth beneath the Earth surface.
    • In the upper part of the crust, temperature increases at an average 3 degrees C for each 100 meters, or 30 degrees C per km of depth.
Card Set
Engineering Geology - Chapter 3 - Igneous Rocks
CHAPTER 3: Igneous Rocks, Intrusive Activity, and the Origin of Igneous Rocks. TOPICS: The Rock Cycle, Igneous Rocks, Identification of Igneous Rocks, Intrusive Bodies, Plutonic Rocks, How Magma Forms, How Magmas of different compositions form.