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Rocks. Ch 5 CP/GHP Book. Extrusive igneous rocks form on or near the surface. Intrusive igneous rocks form below the surface. What are Igneous Rocks?. Form from crystallized magma (lava = magma that flowed out onto Earth’s surface) Ignis is Latin for “fire”
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Rocks Ch 5 CP/GHP Book
Extrusive igneous rocks form on or near the surface. Intrusive igneous rocks form below the surface.
What are Igneous Rocks? • Form from crystallized magma (lava = magma that flowed out onto Earth’s surface) • Ignis is Latin for “fire” • Extrusive (fine-grained, cool quickly) • Intrusive (course-grained, cool slowly)
Magma Composition • O, Si, Al, Fe, Mg, Ca, K and Na • 96% of Earth’s crust is silica (SiO2) • Types of magmaRhyolitic 70%SiO2Andesitic 60%SiO2Basaltic 50%SiO2
Magma Origin • Melting temperatures: 800°C-1200°C • Temperature, pressure, chemical composition and water content all affect magma • Types of Magma
Magma Origin • Geothermal gradient (page 101)
Magma Origin • Melting curve (page 102)
Pause for lab or demo • Bowen’s reaction seriesmelting point of various itemscrystallization point of the same items • Materials:Red, orange and yellow crayonsChocolate chipsLots of gummy bearsCandlesIceHot plate
Results from the lab/demo • Ice begins to melt at 32˚F • Chocolate 70-97˚F • M&M candy shell 98.6˚F • Gummy bears 115˚F • Candles 130˚F • Crayons 145-160˚F
How rocks melt • Partial Melting – process when some minerals melt while others remain solid • Fractional Crystallization – cooling in the reverse order of melting
Bowen’s Reaction Series • Geologist Neil L. Bowenminerals form in predictable patterns
Classifying Igneous Rocks Ch 5.2 • Mineral CompositionFelsic - light colored rocks such as graniteIntermediate - medium colored, andesiteMafic – dark colored rocks such as basaltUltramafic – very high levels of iron, low silica
Classifying Igneous Rocks • Grain Size
Classifying Igneous Rocks • Texture Phaneritic (A)- same size crystals throughoutPorphyritic (B)- large crystals surrounded by finer-grained crystals
Igneous rocks as resources • Ore Deposits • Veins and Pegmatites
Igneous rocks as resources • Kimberlites - ultramafic rocks of peridotite that can contain diamonds