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Lesson 4: Earth Materials

Quartz crystals from TibetThis is the second of three lessons that introduce key geologic topics and provide essential background for the discussions of specific hazards and resources we'll have later in the semester. This week we'll learn about earth materials, the rocks and minerals (like quartz, at right) that are the "buiding blocks" of our planet. In addition to providing many of the critical raw materials on which humanity depends, earth materials also provide important insights into specific geologic processes and hazards. Whether a volcano is likely to erupt effusively or explosively; a town is susceptible to damage from sinkholes; or a roadway can be built safely on a hillside underlain by metamorphic rocks—all of these questions are ones that geologists attempt to answer by studying earth materials.

Developing a working understanding of rocks and minerals in only a week is a tall order, and it's made more difficult in an online class because reading about these materials and looking at pictures of them are not substitutes for actually being able to examine them yourself. Earl Bennett, my boss at the Idaho Geological Survey, used to say, "The best geologist is the one who has seen the most rocks," and there's a lot of truth to that. So, if you live in or near Weed and would like to see some of the common rocks and minerals described in this week's lesson just send me a private message. I'll put together a suite of samples and we'll arrange a time when you can come in and study them. If you live elsewhere you might want to contact a geology instructor at a nearby college or science teacher at a nearby school and ask if you could come in and take a look at the samples he or she might have.

In chapter 3 Keller briefly describes what minerals are and how their properties depend both on their elemental compositions and atomic structures. He goes on to explain that rocks are aggregates of one or more minerals and describes what the characteristics of rocks in each family—igneous, sedimentary and metamorphic—tell us about the conditions under which they formed. For example, coarse-grained igneous rocks crystallized from magmas that cooled slowly deep underground, whereas fine-grained and glassy igneous rocks solidified rapidly from magmas that were erupted onto Earth's surface. Finally, Keller outlines three "rock laws" that enable us to establish the relative ages of adjoining rock units, and describes some common structures—folds, faults and unconformities—that develop where rocks are either deformed within the Earth or deposited at very different times.

As you read through the introduction to earth materials in our text and work through the rock and mineral identification and relative dating exercises online it will be helpful to take careful notes. A lot of information that bears on this week's learning objectives is presented in the chapter, and writing out key facts in your own words or making neatly labeled drawings will help you better understand the significance of what you've read and spot any gaps in your knowledge. Having complete notes will also make it easier for you to review for this week's quiz and and access what you've learned when you want to refer back to it for future assignments. Be sure that you are prepared to meet the learning objectives outlined below before you move on to the quiz at the bottom of the page.

Weekly Learning Objectives

Upon successful completion of this week's lesson, a student is expected to be able to:

Reading and Browsing Assignment

Exercise 4: Rocks, Minerals and Relative Dating (Due by 9:00 AM on 12-Sep-2011)

Exercise 4 will give you an opportunity to demonstrate what you've learned about the identification of rocks and minerals and the sequencing of geologic events using the "rock laws". When you have completed the "Reading and Browsing Assignment" above, point your browser to the class' Etudes site, go to the "Assignments, Tests, and Surveys" tool, and complete Exercise 4.

Quiz 4: Earth Materials (Due by 9:00 AM on 12-Sep-2011.)

After you feel you have met the learning outcomes outlined above, please complete Quiz 4 in the Etudes "Assignments, Tests, and Surveys" tool. There are ten questions, each worth one point. If you can answer all of them correctly it means that you know your way around the basics of Earth materials and relative dating pretty well and are ready to move on to a more detailed look at natural hazards next week.