Ch04_Outline

Ch04_Outline - Chapter 4 Igneous Rocks General...

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1 Chapter 4 Igneous Rocks General characteristics of magma ± Igneous rocks form as molten rock cools and solidifies ± General characteristics of magma Parent material of igneous rocks Forms from partial melting of rocks Magma at surface is called lava General characteristics of magma ± General characteristic of magma Rocks formed from lava = extrusive , or volcanic rocks Rocks formed from magma at depth = intrusive , or plutonic rocks
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2 General characteristics of magma ± The nature of magma Consists of three components: Liquid portion = melt Solids, if any, are silicate minerals Volatiles = dissolved gases in the melt, including water vapor (H 2 O), carbon dioxide (CO 2 ), and sulfur dioxide (SO 2 ) General characteristics of magma ± Crystallization of magma Cooling of magma results in the systematic arrangement of ions into orderly patterns The silicate minerals resulting from crystallization form in a predictable order Texture - size and arrangement of mineral grains Igneous textures ± Texture is used to describe the overall appearance of a rock based on the size, shape, and arrangement of interlocking minerals ± Factors affecting crystal size Rate of cooling Slow rate = fewer but larger crystals Fast rate = many small crystals Very fast rate forms glass
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3 Igneous textures ± Factors affecting crystal size % of silica (SiO 2 ) present Dissolved gases Igneous textures ± Types of igneous textures Aphanitic (fine-grained) texture Rapid rate of cooling Microscopic crystals May contain vesicles (holes from gas bubbles) Phaneritic (coarse-grained) texture Slow cooling Large, visible crystals Aphanitic texture Figure 4.3 A
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4 Phaneritic texture Figure 4.3 B Igneous textures ± Types of igneous textures Porphyritic texture Minerals form at different temperatures Large crystals ( phenocrysts ) are embedded in a matrix of smaller crystals (
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This note was uploaded on 07/17/2008 for the course GS 121 taught by Professor Leavell during the Fall '07 term at Ohio State.

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Ch04_Outline - Chapter 4 Igneous Rocks General...

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