Geology 15                                                                                          West Valley College R. Lopez

Study Questions 4

The Rock Cycle and Igneous Rocks


1)      Read Harden’s discussion of igneous rocks and the rock cycle (p. 18-26, 33-35).

2)      Be able to sketch and discuss the rock cycle diagram (Harden Fig. 2-19).

3)      What is the origin of the term “igneous”, and what do all igneous rocks have in common?

4)      What are sediments, what are they composed of, and where are they deposited?

5)      What is the difference between sediments and sedimentary rock?

6)      What does the process of lithification involve?

7)      What is the most distinctive feature of sedimentary rocks as a group?

8)      What is the origin of the term “metamorphic”, and how do metamorphic rocks form?

9)      Igneous rocks are classified based principally on what two characteristics?

10)  Why is grain size important?  Contrast grain sizes of volcanic and plutonic rocks.

11)  Be able to draw a simple cross-section showing a magma chamber, pluton, sill, dike, and country rock. 

12)  How do sills and dikes differ? 

13)  How do intrusive and extrusive igneous rocks differ?

14)  All igneous rocks share what common characteristic?

15)  What is a batholith?  Name one batholith in California.

16)  Describe a porphyritic texture, and what does it tell you about the cooling history of the rock?

17)  Name the principal igneous rock-forming silicate minerals, and group them as “light” or “dark” minerals.

18)  Know the igneous rock classification chart like I did in lecture, including compositional terms such as felsic (silicic) and mafic.  Know the directions that SiO2, FeO, dark minerals, and light minerals increase or decrease according to rock type on the chart.

19)  Peridotite is important for at least two reasons.  What are they?

20)  What is the most abundant type of volcanic rock on earth?  Be able to make a simple cross-section sketch of oceanic crust at a mid-ocean ridge and show where basalt and gabbro are found.  What are pillow basalts and what is their significance?  (See Harden, Figs. 9-4, 12-12, and 16-28).

21)  What is magnetite, Earth’s Magnetic Field, and the Curie point?

22)  What is paleomagnetism and inclination?

23)  If a lava solidifies at the equator, what will be the declination?  If the lava solidifies near 45° North latitude, what will be the inclination?

24)  Be able to sketch the plate tectonic setting of the common rock types (granite, rhyolite, granodiorite, andesite, diorite, basalt, and gabbro) and say a few words about their origin.