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Igneous Rocks Igneous Metamorphic Sedimentary 3 types of rocks Igneous rocks are formed from molten rocks that has cooled and hardened. Ship Rock, New Mexico Formed when magma in a volcano cooled slowly Igneous Rocks Magma (or Lava) cool and crystallize to form igneous rock. Igneous Rocks There are two types of Igneous Rock. Intrusive and Extrusive Igneous Rocks Extrusive Igneous Rock is formed from lava, which is on the surface. Intrusive Igneous Rock is formed from magma, which is below the surface. What is the difference between magma and lava? Lava is on the earth surface and magma is below. Molten rock that flows on the surface of the Earth is lava. Molten rock that is below the surface of the Earth is Magma. Intrusive— large crystals ◦ WHY? The inside of the Earth is VERY hot! Therefore, the magma cools slowly creating larger crystals Extrusive— small crystals ◦ WHY? Earth’s surface is much cooler, and lower temperatures mean rocks cool quickly, not leaving enough time for large crystals to form. Textures of Igneous Rocks Igneous rocks are dominated by silicate minerals. Silicates Molten rock with lower amounts of silica flows faster than molten rock with higher amounts of silica. If lava has more silica, it will move slower than lava with less silica. Lava spread = small amounts of silica Explosive eruptions = large amounts of silica Extrusive Igneous Formations Where are many Igneous Rocks found? Divergent boundaries and volcanoes. Igneous rock undergoes weathering (or breakdown) to form sediment. So it becomes…………………… ◦ Sedimentary Rock The Rock Cycle Of the following three types of rocks, igneous rocks are the hardest. Igneous Rocks Stone Mountain The Stone Mountain granite is a relatively small granite pluton that covers an area less than a county in size. Stone Mountain Stone Mountain is made of granite and is an igneous rock. Stone Mountain Magma that cools and hardens forms an intrusive igneous rock Lava that cools and hardens forms an extrusive igneous rock