Section Assessment

Section Summary

I Magma consists of molten rock, dissolved gases, and mineral crystals.

I Magma is classified as basaltic, andesitic, or rhyolitic, based on the amount of silica it contains.

I Different minerals melt and crystallize at different temperatures.

I Bowen's reaction series defines the order in which minerals crystallize from magma.

Understand Main Ideas

1. main<TTflH Predict the appearance of an igneous rock that formed as magma cooled quickly and then more slowly.

2. List the eight major elements present in most magmas. Include the chemical symbol of each element.

3. Summarize the factors that affect the formation of magma.

4. Compare and contrast magma and lava.

Think Critically

5. Predict If the temperature increases toward the center of Earth, why does the inner core become solid?

6. Infer the silica content of magma derived from partial melting of an igneous rock. Would it be higher, lower, or about the same as the rock itself? Explain.

CEZES^Earth Science

7. A local rock collector claims that she has found the first example of pyroxene and sodium-rich feldspar in the same rock. Write a commentary about her claim for publication in a rock collector society newsletter.

Earth b Sclartt^

Self-Check Quiz glencoe.com

Section 1 • What are igneous rocks? 117

Douglas P. Wilson; Frank Lane Picture Agency/CORBIS

Earth b Sclartt^

Self-Check Quiz glencoe.com

Section 1 • What are igneous rocks? 117

Douglas P. Wilson; Frank Lane Picture Agency/CORBIS

Section 5.2

Objectives

I Classify different types and textures of igneous rocks. I Recognize the effects of cooling rates on the grain sizes in igneous rocks.

I Describe some uses of igneous rocks.

Review Vocabulary fractional crystallization:

a sequential process during which early formed crystals are removed from the melt and do not react with the remaining magma.

New Vocabulary intrusive rock extrusive rock basaltic rock granitic rock texture porphyritic texture vesicular texture pegmatite kimberlite

Figure 5.8 Differences in magma composition can be observed in the rocks that form when the magma cools and crystallizes. Observe Describe the differences you see in these rocks.

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