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Chapter 5 “Igneous Rock”
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Objectives Describe how the cooling rate of magma & lava affects the texture of igneous rocks. Classify igneous rocks according to their mineral composition. Describe a number of identifiable rock structures.
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2 types of Igneous Rocks Intrusive Extrusive Created inside the earth
Created on top of the ground
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Intrusive Igneous Rocks
Magma cools slowly underground Creates large, well-developed crystals Example: Granite
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Extrusive Igneous Rocks
Extrusive Igneous Rocks Created when lava cools rapidly Examples: Basalt (oceans) Obsidian (glass) Pumice (has gas bubbles)
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What happens if the outside cools rapidly – but the inside cools slowly?
Creates a rock with a porphyritic texture. Small crystals outside Quickly formed Larger crystals embedded inside Formed slowly
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Mineral Composition of Igneous Rocks
#1 Felsic High in silica (SiO) Examples: Feldspar, quartz, mica Granite, Rhyolite, Obsidian #2 Intermediate #3 Mafic
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Mineral Composition of Igneous Rocks (cont.)
#2 Intermediate Medium colored (grays/browns/reds) Pink Feldspar Diorite, Andesite
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Mineral Composition of Igneous Rocks (cont.)
#3 Mafic Rich in Magnesium & Iron Heavy & dense Olivine, Hornblende Basalt, Gabbro
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Igneous Rock Structures
3rd start here wed Igneous Rock Structures Intrusions Formed inside the earth Extrusions Formed on the surface
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Igneous Intrusions Batholiths
Means “deep rock” Large igneous formations Must be over 100 km2 The continents are underlain by large batholiths Similar, smaller areas are called “stocks”
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Intrusions (cont.) Laccolith Means “layer of rock” Found in groups
Bubbles of magma that have cooled underground Usually mushroom shaped
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Intrusions (cont.) Sill Dikes A flat layer of solidified magma
Vertical columns of solidified magma
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Igneous Extrusions Volcanic Neck What’s left of an ancient volcano
May also include exposed fingers of hardened lava known as dikes
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Igneous Extrusions (cont.)
Lava flows Flat layers of solidified lava
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Igneous Extrusions (cont.)
Lava plateau Wide, flat areas of hardened lava
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Assignments: Complete Chapter 4 interactive notes for Homework
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Intrusive VS Extrusive
Groups Felsic Intermediate Mafic Intrusive VS Extrusive
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