Presentation on theme: "CH. 5 – Igneous Rocks What are igneous rocks? Formed by the hardening of magma. “Ignis” means fire What is the difference between magma."— Presentation transcript:
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)
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.
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
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
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)