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Chapter 2: Rocks: Section 2: Igneous Rock Origins of Igneous Rock Igneous- Latin word for “fire.” Magma cools into various types of igneous rocks depending two things 1) the composition of the magma 2) the amount of time it takes the magma to cool and solidify Three ways magma is formed 1) rock is heated 2) pressure is released 3) when rock changes composition Name ____________________________________ #_______ date _____________ Extrusive Igneous Rock Composition and Texture of Igneous Rock Igneous Rock Formations Igneous rocks are divided into two groups based what the rock is mad of and how fast they cooled. When magma cools beneath the Earth’s surface this is called intrusive rock. When magma cools on the Earth’s surface this is called extrusive rock. Felsic: Light-colored rocks and less dense. Intrusive rock- Extrusive rock- Rich in elements such as silicon, aluminum, sodium, and potassium. Mafic: Dark-colored rocks and are denser. Rich in elements such as iron, magnesium, and calcium **The longer it takes for magma or lava to cool, the more time mineral crystals have to grow. The more time they have to grow the coarser the texture of the igneous rock that is formed. Usually has a coarsegrained texture. When the magma cools it is surrounded by rock and cools slowly. They are named for their size and the way they intrude to push into the surrounding rock. Plutons Dike Volcanic neck Sill Batholith Laccolith Most volcanic rock is extrusive. Extrusive rock cools quickly on the surface and contains very small crystals or none at all. When lava erupts from a volcano a formation called lava flow is made. Sometimes lava comes from long cracks in the Earth called fissures. These can cover a vast area making a lava plateau.