22.3 Rocks and the Rock Cycle
Reading Focus
Key Concepts
What are the three major groups of rocks?- How do igneous rocks form?
- How are sedimentary rocks classified?
- How do metamorphic rocks form?
- How can one type of rock change into another?
Vocabulary
igneous rock
magma
lava
intrusive rock
extrusive rock
sediment
sedimentary rock
clastic rocks
metamorphic rock
foliated rocks
rock cycle
Reading Strategy
Comparing and Contrasting Copy the table below. After you read, compare groups of rocks by completing the table.
Rock Group |
Formed by |
Example |
|---|---|---|
Igneous |
a. |
b. |
c. |
d. |
Sandstone |
e. |
Heat and pressure |
f. |
Towering more than 1000 meters above Yosemite Valley, California, the steep rock face of El Capitan attracts rock climbers from around the world. In 1993, climber Lynn Hill accomplished the first “free climb” of El Capitan. That is, she climbed without the aid of a rope, except to provide safety in case of a fall. Over four days, Hill ascended El Capitan's steep “nose route,” with its sheer cliffs and many overhangs. For an encore, she climbed the same route in 1994 in less than 24 hours!
Figure 14 Lynn Hill is climbing the face of this rock.
El Capitan is one of the largest and most impressive chunks of granite on Earth. Yet each of the much smaller rocks that we pass every day also has a fascinating story to tell. Was it formed deep inside a volcano, or crushed by tremendous forces deep within Earth? A few easy-to-observe properties can reveal much about a rock's history.
Classifying Rocks
The properties that geologists use to identify rocks include color and crystal size. The color of a rock indicates the minerals it contains. However, because the colors of most minerals can vary, a rock's color is not always a reliable way to identify it. A better way to identify rocks is by the size of the crystals or other particles they contain.
The size, shape, and arrangement of the crystals and other particles that make up a rock give the rock its texture. A rock's texture reveals what the rock is made from and how and where it formed. Rocks are classified into three major groups—igneous, sedimentary, and metamorphic—based on how they form.
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