G Study Guide

BIG (Idea

Igneous rocks were the first rocks to form as Earth cooled from a molten mass to the crystalline rocks of the early crust.

Vocabulary

Key Concepts

What are igneous rocks?

Bowen's reaction series (p. 114) fractional crystallization (p. 115) igneous rock (p. 112) lava (p. 112) partial melting (p. 114)

MAUWJdSa Igneous rocks are the rocks that form when molten material cools and crystallizes.

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

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

• Different minerals melt and crystallize at different temperatures.

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

Bowen Reaction Series

.2 Classification of Igneous Rocks

Section basaltic rock (p. 118) extrusive rock (p. 118) granitic rock (p. 118) intrusive rock (p. 118) kimberlite (p. 123) pegmatite (p. 122) porphyritic texture (p. 120) texture (p. 119) vesicular texture (p. 120)

IMAGES Classification of igneous rocks is based on mineral composition, crystal size, and texture.

• Classification of igneous rocks is based on three main characteristics.

• The rate of cooling determines crystal size.

• Ores often occur in pegmatites. Diamonds occur in kimberlites.

• Some igneous rocks are used as building materials because of their strength, durability, and beauty.

126 Chapter 5 • Study Guide

(t)Marli Miller/Visuals Unlimited, (b)Albert J. Copley/Visuals Unlimited

126 Chapter 5 • Study Guide

(t)Marli Miller/Visuals Unlimited, (b)Albert J. Copley/Visuals Unlimited

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