Essentials of Geology (10th Edition)

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Unformatted text preview: Essentials of Geology I gneous Rocks Chapter 3 Char acter istics of magma • I gneous r ocks for m as molten r ock cools and solidifies • Gener al Char acter istic of magma • Par ent mater ial of igneous r ocks • For ms fr om par tial melting of r ocks inside Ear th • M agma that r eaches the sur face is called lava Mount Rushmore (Granite) Obsidian I gneous r ocks I gneous r ocks for m when magma magma cools and solidifies at or below the sur face magma magma … • is molten molten (melted) silicate r ock • contains dissolved gases (mainly H 2 O , CO 2 , and SO 2 ) and often contains cr ystals • often is less dense than sur r ounding r ock and will r ise though the cr ust Char acter istics of magma • The natur e of magma • Consists of thr ee components: – A liquid por tion, called melt , that is composed of mobile ions – Solids , if any, ar e silicate miner als that have alr eady cr ystallized fr om the melt – Volatiles , which ar e gases dissolved in the melt, including water vapor (H 2 O), car bon dioxide (CO 2 ), and sulfur dioxide (SO 2 ) A cooling magma will begin to cr ystallize as atoms for m chemical bonds and build cr ystals of var ious silicate miner als (ex. feldspar feldspar ) M any types of igneous r ock exist (ex. andesite andesite ) because of var iations in magma composition and r ates of cr ystallization. Two main gr oups… intr usive or plutonic plutonic igneous r ocks for m by magma cooling slowly below the sur face extr usive or volcanic igneous r ocks for m by magma (lava) cooling Granite Granite El Capitan El Capitan Yosemite N.P., CA Yosemite N.P., CA Basalt Lava Flow Basalt Lava Flow H awaii H awaii Char acter istics of magma • Cr ystallization of magma • Textur e in igneous r ocks is deter mined by the size and ar r angement of miner al gr ains • I gneous r ocks ar e typically classified by – Textur e – M iner al composition Classify and name igneous r ocks using: 1) textur e 2) miner al compositio n I gneous textur es • Textur e is used to descr ibe the over all appear ance of a r ock based on the size, shape, and ar r angement of inter locking miner als • Factor s affecting cr ystal size • Rate of cooling – Slow r ate pr omotes the gr owth of fewer but lar ger cr ystals 1) Textur e = size, shape, and distr ibution of mater ial composing a r ock Rate of cooling is the main contr ol on cr ystal size: slower = mor e time = lar ger cr ystals = a coar se-gr ained or phaner itic textur e Gr anite typically has a phaner itic textur e I gneous textur es • Types of igneous textur es • Aphanitic (fine-gr ained) textur e – Rapid r ate of cooling of lava or magma – M icr oscopic cr ystals – M ay contain vesicles (holes fr om gas bubbles) • Phaner itic (coar se-gr ained) textur e – Slow cooling – Cr ystals can be identified without a micr oscope Fine-gr ained textur e Coar se-gr ained textur e...
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This note was uploaded on 06/15/2011 for the course GEL 111 taught by Professor Vandevelde during the Spring '11 term at Craven CC.

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Ch 03 - Essentials of Geology I gneous Rocks Chapter 3 Char...

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