Chapter 3 - Igneous Rocks

Chapter 3 - Igneous Rocks - Chapter3Review(Bold print...

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Chapter 3 Review  (Bold print indicates potential quiz question) (1) Igneous rocks form when magma cools and solidifies. Extrusive, or volcanic, igneous rocks result when lava cools at the surface. Magma that solidifies at depth produces intrusive, or plutonic, igneous rocks. (2) As magma cools, the ions that compose it arrange themselves into orderly patterns during a process called crystallization. Slow cooling results in the formation of rather large crystals. Conversely, when cooling occurs rapidly, the outcome is a solid mass consisting of tiny intergrown crystals. When molten material is quenched instantly, a mass of unordered atoms, referred to as glass forms. (3) Igneous rocks are most often classified by their texture and mineral composition. (4) The texture of an igneous rock refers to the overall appearance of the rock based on the size and arrangement of its interlocking crystals. The most important factor affecting texture is the rate at which magma cools. Common igneous rock textures include aphanitic (rapid cooling) , with grains too small to be distinguished without the aid of a microscope; phaneritic (slow cooling) , with intergrown crystals that are roughly equal in size and large enough to be identified with the unaided eye; porphyritic (differing rates) , which has large crystals (phenocrysts) interbedded in a matrix of smaller crystals (groundmass); and glassy (very rapid cooling) . (5) The mineral composition of an igneous rock is the consequence of the
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This note was uploaded on 03/30/2011 for the course GEOL 101 taught by Professor Galland during the Fall '08 term at BYU.

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Chapter 3 - Igneous Rocks - Chapter3Review(Bold print...

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