Igneous Rocks © Copyright NewPath Learning. All Rights Reserved. 94-4671 Visit www.newpathlearning.com for Online Learning Resources. magma lava Formation of Igneous Rock Igneous rocks form from cooling magma and lava. They are classified according to their mineral origin, texture and composition. The origin of igneous rocks is either intrusive or extrusive. Cooling magma below the Earth’s surface forms intrusive rocks, while erupting lava forms extrusive igneous rocks. Classifying Igneous Rocks The texture of an igneous rock is related to how long it takes to cool. Slow-cooling rock forms more crystals and is coarse-grained, while fast-cooling rock has fine grain. Intrusive Extrusive basalt pumice granite magma chamber magma obsidian Extrusive Intrusive Dark igneous rocks, referred to as mafic, have high concentrations of calcium, iron and magnesium. Light igneous rocks are described as felsic, and they have high concentrations of silica, aluminum and potassium. Basalt is a dark igneous rock with visible crystals. It is the most common extrusive rock, forming most of the ocean’s crust. Obsidian is a dark, glassy, extrusive igneous rock. It cools so quickly that it does not have visible crystals. When lava froths up with gases, a lightweight rock called pumice is formed. It is the only rock that can float on water. Granite is a light colored intrusive igneous rock with visible crystals. It is an abundant rock, found at the core of most mountains. lava quartz silica 50-70 % silica
Pause and Review Describe the composition, texture and origin of these igneous rocks. Igneous Rocks Color Classication Origin Example Mineral Concentrations obsidian basalt granite IGNEOUS ROCKS pumice © Copyright NewPath Learning. All Rights Reserved. 94-4671 Visit www.newpathlearning.com for Online Learning Resources.