Earth Science::Igneous Rocks
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37 terms
Terms | Definitions |
|---|---|
 Igneous Rocks | Cooling and solidification of magma. -ex] granite and basalt |
| Magma | Formed by melting of rocks in the hot deep crust and mantle. -called lava when at Earth's surface. |
| Crystallization of Magma | -water changes from liquid to solid at 0%C -magma changes from liquid to solid over a temp interval of 200-300 C -as magma cools, different silicate minerals begin to crystallize and grow. |
| Igneous Rocks | extrusive::volcanic intrusive::plutonic |
| Extrusive or Volcanic Rocks | Formed from lava at the Earth's surface. |
| Intrusive or Plutonic Rocks | Formed from magma at depth. |
| Magma | Consists of three components: -liquid -solid -gases |
| Melt | The liquid portion of magma. |
| Silicate Minerals | The solid portion of magma. |
| Volatiles | Gases including water (H2O), carbon dioxide, sulfur dioxide. -at high pressures at depth in magma=dissolved in the melt. -at low pressures near surface=form separate gas phase. |
| Classifying Igneous Rocks | -texture -types of minerals -chemical composition |
| Igneous Textures | Aphantic Phaneritic Pegmatic Pyroclastic Glassy |
| Aphantic | -Fine-grained rock. -Crystals too small to identify with naked eye. (<1mm) -Rapid rate of cooling near surface: volcanic -May contain vesicles(holes from gas bubbles) |
| Phaneritic | -Coarse-grained rock. -Large visible crystals. (c. 1-20 mm) -Slow rate of cooling at depth: plutonic |
| Porphyritic | -Large crystals (phenocrysts) are embedded in a matrix of smaller crystals (groundmass) -Minerals form at different temperatures. |
| Pegmatic | -Extremely coarse-grained rock. -Crystal sizes from several cm to several m. -Form in late stages of crystallization of magma when rich in fluids (H2O) |
| Pyroclastic | -Also known as fragmental texture. -Produced by violent volcanic eruptions. -Often appear more similar to sedimentary rocks. -Tuff= ash-sized fragments (<2mm) -Volcanic breccia=particles larger than ash. |
| Glassy | -Very rapid cooling lava resulting rock is called obsidian. -Used by many ancient cultures to make sharp blades and arrowheads. -ex] pumice: frothy glass. |
| Pumice | -Depressurization forms bubbles in the magma as gases exsolve, rapid cooling freezes the bubbles in glass. -uses: abrasive & cement additive. |
| Minerals in Igneous Rocks | Silicate minerals are the most important constituents. -silicon-oxygen tetrahedron is the fundamental building block. |
| Ferromagnesian | Dark, mafic -silicates: olivine, pyroxene, amphibole, and biotite mica. |
| Nonferromagnesian | Light, felsic -silicates: quartz, muscovite mica, and feldspars. |
| Granitic Composition | -Mainly light-colored silicates. -Felsic (FELdspar & SIlica) in composition. -Major constituent of continental crust. |
| Basaltic Composition | -Dark silicates and calcium-rich feldspar. -Mafic (MAgnesium & FErrum, for iron) in composition. -Major constituent of oceanic crust. |
| Felsic | Granite (plutonic) Rhyolite (volcanic) -high sticky |
| Intermediate | Diorite (plutonic) Andesite (volcanic) |
| Mafic | Gabbro (plutonic) Basalt (volcanic) -low runny |
| Earth's mantle | Ultramafic |
| Basaltic Composition | viscosity: low (runny) |
| Rhyolitic | viscoscity: high (sticky) |
| Origin of Magma | -The Earth's crust and mantle are solid rocks. -Earth's crust does NOT float on Mantle of molten rock. -Magma only forms in special places where conditions allow pre-existing solid rocks to melt. |
| Origin of Magma | Three Ways: 1. Increase temperature (thermal) 2. Decrease pressure (decompression) 3. Add water (fluid-induced) -most magma formed from melting of mantle but some felsic rocks from melting of crust. |
| Decompression Melting | A decrease in confining pressure causes a decrease in a rock's melting temperature. -divergent plate margins along mid-ocean ridges. |
| Fluid-Induced Melting | Adding volatiles (primarily water) causes rocks to melt at lower temperatures. -convergent plate margins along subduction zones. |
| Magmatic Differentiation | During crystallization, the composition of the liquid portion of the magma continually changes. -composition of magma in chamber changes as crystals grow and are then removed by settling. |
| Magma Compositional Variations | A single volcano may erupt lavas with very different compositions. -ex] Crater Lake, Oregon |
| Ore Deposits | Economically-viable sources for many metals. -ex] chromium, platinum, gold, copper, nickel. |
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