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OVERVIEW

Some of the most recent and revolutionary ideas of science have been developed in the earth sciences. The
revolution began with the understanding that parts of Earth’s surface are continually moving. This led to a new
theory about Earth’s surface consisting of moving plates. The new theory brought together the dynamics of moving
continents, ocean basins that are constantly being created and destroyed, and a crust that is subjected to volcanoes
and earthquakes. The creation of new ideas continued as scientists began to understand that the separate parts
of Earth—the interior, the surface, the atmosphere, and the water on the surface—are all engaged in an ongoing
cycling of materials (Figure 17.1).
The fascinating story of Earth’s unique, unified cycles continues over the ensuing chapters. The story begins
with this chapter on rocks and minerals, the basic materials that make up Earth. This is followed by evidence from a
number of sources that is used to describe how Earth’s interior is arranged, as well as how rocks and minerals cycle
into and out of the interior. Evidence from the ocean then leads to a theory about plates that move on the surface.
Next, you will learn how rocks are folded, faulted, and sculptured to produce the landscape you see on Earth today.
Understanding the sculpting process will enable you to interpret the landscape where you live for meaning about
Earth’s past and perhaps its future.
As you can see, Earth is not made of isolated, independent parts. All parts of this dynamic Earth are related, and
changes in one part affect the other parts. Yet, in spite of all the changes and cycles, each part of Earth has remained
amazingly stable for millions of years. The study of earth science is thus viewed in a broad context, a context that will
help you to understand Earth where you live, as well as present-day environmental concerns. Understanding all this
starts with the basic materials of Earth—rocks and minerals—the subject of this chapter.

Earth’s crust that are known as minerals and rocks. For now,
17.1 SOLID EARTH MATERIALS
consider a mineral to be a solid material of Earth that has
Earth, like all other solid matter in the universe, is made up of both a known chemical composition and a crystalline struc-
chemical elements. The different elements are not distributed ture that is unique to that mineral. About 2,500 minerals
equally throughout the mass of Earth, however, nor are they are known to exist, but only about 20 are common in the
equally abundant. As you shall see in chapter 18, there is evidence crust. Examples of these common minerals are quartz, calcite,
that Earth was molten during an early stage in its development. and gypsum.
During this molten stage, most of the heavier abundant elements, Minerals are the fundamental building blocks of the rocks
such as iron and nickel, apparently sank to the deep interior of making up Earth’s crust. A rock is a solid aggregation of one or
Earth, leaving a thin layer of lighter elements on the surface. This more minerals that have been cohesively brought together by a
thin layer is called the crust. The rocks and rock materials that rock-forming process. There are many possibilities of different
you see on the surface and the materials sampled in even the kinds of rocks that could exist from many different variations
deepest mines and well holes are all materials of Earth’s crust. of mineral mixtures. Within defined ranges of composition,
The bulk of Earth’s mass lies below the crust and has not been however, there are only about 20 common rocks making up the
directly sampled. crust. Examples of common rocks are sandstone, limestone, and
Chemical analysis of thousands of rocks from Earth’s sur- granite.
face found that only eight elements make up about 98.6 per- How the atoms of elements combine depends on the num-
cent of the crust. All the other elements make up the remaining ber and arrangement of electrons around the atoms. How they
1.4 percent of the crust. Oxygen is the most abundant element, form a mineral, with specific properties and a specific crystal-
making up about 50 percent of the weight of the crust. Silicon line structure, depends on the electrons and the size of the ions
makes up over 25 percent, so oxygen and silicon alone make up as well. A discussion of the chemical principles that determine
about 75 percent of Earth’s solid surface. the structure and properties of chemical compounds is found
Figure 17.2 shows the eight most abundant elements that in chapters 8 and 9 of this book. You may wish to review these
occur as elements or combine to form the chemical com- principles before continuing with the discussion of common
pounds of Earth’s crust. They make up the solid materials of minerals and rocks.

434 CHAPTER 17 Rocks and Minerals 17-2