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