PSNB+5.2

toc =5.2 Igneous Rocks (pg. 140)=

Vocabulary

 * Extrusive Rock:** An igneous rock that is created when lava erupts on the surface of earth.
 * Intrusive Rock:** An igneous rock that is created from hardened magma below the surface of earth.
 * Porphyritic Texture:** The texture of an igneous rock, where big crystals are spread behind much smaller crystals.

Characteristics of Igneous Rock

 * Igneous rock forms from lava or magma
 * Most igneous rocks are made of mineral crystals
 * Origin**
 * Igneous rocks are classified according to where they formed
 * Extrusive: lava on earth's surface
 * Intrusive: magma below earth's surface
 * Texture**
 * Fast-cooling creates fine grained rocks
 * Porphyritc forms when first magma cools slowly, then remaining magma cools fast
 * Mineral Composition**
 * Lava high in silica makes light colored rocks (granite)
 * Lava low in silica makes dark-colored rocks (basalt)
 * Color varies on mineral amounts

Uses of Igneous Rocks

 * Many Igneous rocks are hard, dense, and durable
 * Granite has long history as building material
 * Many different countries and states used it for different things
 * other igneous rocks also have important uses

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