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CH. 5 – Igneous Rocks

CH. 5 – Igneous Rocks. What are igneous rocks? Formed by the hardening of magma. “Ignis” means fire What is the difference between magma & lava? Lava is magma above ground. Types of Igneous Rock 1. Extrusive – fine-grained igneous rocks that cool quickly on Earth’s surface.

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CH. 5 – Igneous Rocks

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  1. CH. 5 – Igneous Rocks What are igneous rocks? Formed by the hardening of magma. “Ignis” means fire What is the difference between magma & lava? Lava is magma above ground. Types of Igneous Rock 1. Extrusive – fine-grained igneous rocks that cool quickly on Earth’s surface. Ex. Rhyolite (pg.100) 2. Intrusive – coarse-grained igneous rocks that cool slowly below the Earth’s surface. Ex. Granite (pg. 100)

  2. Composition of Magma • Magma is classified based on the amount of silica it has. • Table 5-1 (pg. 101) • 1. Rhyolitic – 70% Silica • 2. Andesitic – 60% Silica • 3. Basaltic – 50% Silica • How does magma form? • Heat and pressure under the Earth’s surface. • Where does the heat come from? • The decay of radioactive elements. • The pressure increases the heat & the deeper below the Earth’s surface the greater the pressure, thus more heat. • Temperatures must reach 800°C to 1200°C before rocks start to melt. These temperatures occur in the upper mantle and lower crust.

  3. Factors that affect magma formation • Temperature, pressure, water content, and mineral composition. • Partial melting – mineral melt at various temperatures, thus some may become liquids while other remain solids in rock formations. • Fractional crystallization – the process by which different minerals form at different temperatures. • Bowen’s reaction series – the concept that magma cools & forms minerals at predictable patterns. • Fig 5-6 (pg. 104) – Go Over

  4. Classifying Igneous Rocks • Mineral Composition • 3 Main Groups – Table 5-2 (pg. 107) • 1. Felsic – light-colored, have high silica contents, and contain quartz and the feldspars orthoclase and plagioclase. • 2. Mafic – dark-colored, have lower silica contents, and contain lots of iron and magnesium. It also contains plagiocas, biotite, amphibole, pyroxene, and olivine. • 3. Intermediate – In between the two. • 4. Ultramafic Rocks – rocks with low silica contents and very high levels of iron and magnesium. • Peridotite and dunite  pg. 108 – fig. 5-10

  5. Porphyritic is a rock with texture with large crystals surround by finer-grained crystals. • Fig. 5-13 (pg. 110) • Pegmatites have veins of extremely large-grained minerals. • Fig 5-16 (pg. 112) • Kimberlites are rare ultramafic rocks that have diamonds embedded in them. • Most diamonds come from mines in South Africa • Fig. 5-17 (pg. 113)

  6. TYPES OF IGNEOUS ROCKS • 1. Obsidian • 2. Pumice • 3. Scoria • 4. Rhyolite • 5. Andesite • 6. Basalt • 7. Gabbro • 8. Diorite • 9. Granite • 10. Biotite Granite

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