CH. 5 – Igneous Rocks What are igneous rocks? Formed by the hardening of magma. 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)

Where does the heat come from? 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 increase the heat & the deeper below the Earth’s surface the greater the pressure, thus more heat.

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)

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.

Pegmatites have veins of extremely large-grained minerals. 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)