Chapter Overview

This chapter is the first of six on the material of which Earth is made. The following chapters are mostly about rocks. Nearly all rocks are made of minerals. Therefore, to be ready to learn about rocks, you must first understand what minerals are as well as the characteristics of some of the most common minerals.

In this chapter, you are introduced to some basic principles of chemistry (this is for those of you who have not had a chemistry course). This will help you understand material covered in the chapters on rocks, weathering, and the composition of Earth's crust and its interior. You will discover that each mineral is composed of specific chemical elements, the atoms of which are in a remarkably orderly arrangement. A mineral's chemistry and the architecture of its internal structure determine the physical properties used to distinguish it from other minerals. You should learn how to readily determine physical properties and use them to identify common minerals. (Appendix A of your text is a further guide to identifying minerals).

Learning Objectives

1. Rocks are naturally formed, consolidated material composed of grains of one or more minerals. Minerals are crystalline (orderly three-dimensional arrangements of atoms).

2. Elements are substances that cannot be broken down by ordinary chemical methods. Atoms are the smallest particles of elements. They are constructed of protons, neutrons (forming the nucleus) and electrons. Atomic mass number, atomic number and atomic weight control the"character" of an element, particularly its isotopes.

3. Chemical activity is related to ions and their bonding.

4. Eight elements comprise 98% of the weight of the crust. Oxygen accounts for half the weight of the crust. Silicon is the second most abundant element in the crust and silicate minerals, combinations of oxygen and silicon, are the most common in the crust.

5. Crystalline substances have a three-dimensional, regularly repeating, orderly pattern of their anions. The silica tetrahedron is the basic "building block" of most common (silicate) minerals. Silicate structure reflects the arrangement of silica tetrahedra and the numbers of shared oxygens. These structures include: isolated silicate structure (no shared oxygens), chain-silicates (two shared oxygens), sheet silicates (three shared oxygens), and framework silicates (four shared oxygens).

6. Minerals are naturally occurring solids that are crystalline (which is to say that they have a periodically repeating arrangement of atoms) and have a specific chemical composition. Specific chemical composition reflects the orderly internal arrangement of atoms. Zoning further reflects the orderly arrangement.

7. A small number of rock-forming minerals comprise most of the crust. Five mineral groups (feldspar, quartz, pyroxene, amphibole, and mica) account for greater than 90% of the earth's crust. Feldspars are the most common crustal mineral, while olivine is the most abundant mineral in the earth as a whole. Nonsilicates are either native elements or are classified by their negative ion. These include ore minerals of commercial value.

8. Physical properties are used to identify minerals. These include color, streak, luster, hardness, external crystal form, cleavage, fracture, specific gravity, special properties (smell, taste, striations, magnetism), and other properties (double refraction, effects of polarized light, x-ray defraction). Chemical tests can be used to identify minerals.

Related Readings

Blackburn, W. H., and W. H. Dennen. 1993. Principles of Mineralogy. 2d ed. Dubuque, IA: Wm. C. Brown Publishers.

Chesterman, C. W. 1978. The Audubon Society Field Guide to North American Rocks and Minerals. New York: Alfred A. Knopf.

Gaines, R. V., H. C. W. Skinner, E. E. Foord, B. Mason, and A. Rosenzweig. 1997. Dana's New Mineralogy, 8th ed. Somerset, NJ: John Wiley and Sons.

Klein, C., and C. S. Hurlbut. 1993. Manual of Mineralogy (after J. D. Dana). 21st ed. New York: John Wiley and Sons.

Prinz, M., G. Harlow, and J. Peters. 1978. Simon and Schuster's Guide to Rocks and Minerals. New York: Simon and Schuster.

Schumann, W. 1993. Handbook of Rocks, Minerals and Gemstones. New York: Houghton Mifflin Co.

Answers to EOC Questions

Following are answers to the End of Chapter Questions for Chapter 2:

Boxed Readings