Department of Earth Science |Northeastern Illinois University

ESCI 121
Spring 2007

Daily Objectives #9
(February 14, 2007)                                                                        Dr. Sanders

Homework  #3 (see the homework page) is due today!

By the end of today’s class, you should be able to do the following:

Sedimentary Rocks

* List the two main groups of sedimentary rocks. 

* For each group, explain how rocks in that group form, list a few names of rocks that fall into that group, tell what minerals make up that rock (for the chemical sedimentary rocks), tell what the grain size of sediments is (for the detrital sedimentary rocks), and tell how you might recognize each of the rocks when you see them again.

Igneous Rocks

* Sketch a "melting curve" on a graph with axes showing temperature and pressure.  Show on which sides of the curve liquids and solids would exist.

* Use the melting curve you sketched to illustrate the three processes that lead to melting of rock material:

       - thermal melting (increasing heat)
       - decompression melting (reducing pressure)
       - shifting the position of the melting curve by introducing volatiles (i.e., water)

* Describe the three general settings in which volcanoes are found in the world, and for each, use the melting curve to explain how/why magma forms in that setting:

       - divergent plate boundaries
       - subduction zones
       - hot spots

* Explain the relationship between cooling rate and crystal size in an igneous rock.

* Using the hand samples of igneous rocks in a rock box,  tell which of them cooled relatively slowly, quickly, and instantaneously.

* Explain the difference between granitic (felsic) composition and basaltic (mafic) composition, and how to recognize each type in a hand sample.

* Describe the unique characteristics, including crystal size and composition,  of each of the following igneous rocks:
               - granite         - gabbro       - rhyolite         - basalt       - pumice        - obsidian

Department of Earth Science | Northeastern Illinois University

© 2007 Laura L. Sanders.  Last updated February 14, 2007.