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http://www.videojug.com/film/geology-igneous-rocks http://www.ehow.co.uk/video_4774969_identifying-igneous-rocks.html Vocabulary Magma Molten rock beneath Earth’s surface Lava Molten rock that reaches Earth’s surface through a volcano Igneous Rocks… Formation Cooling Time Crystal Size Mineral Composition Color Origin Igneous Rocks are classified on what minerals make up the rock and the size of mineral crystals. Origin of Igneous Rocks Igneous rocks are classified as INTRUSIVE or EXTRUSIVE Intrusive Forms when magma cools within Earth Magma cools slowly being exposed to high temperatures Reach surface when forces inside Earth push rocks up & wind and water break apart/carry away surface rocks Extrusive Forms when lava cools on Earth’s surface Lava cools quickly being exposed to cool temperatures Reach surface through volcanoes erupting Intrusive Igneous Rocks Forms from magma within Earth’s surface Granite Peridotite Diorite Anorthosite Gabbro Pegmatite Extrusive Igneous Rocks Forms from lava on Earth’s surface Basalt Rhyolite Pumice Andesite Obsidian Scoria Textures of Igneous Rocks Texture of an igneous rock is determined by the size of its mineral crystals. Size of mineral crystals depends on how quickly the magma or lava cools. Textures of Igneous Rocks Intrusive Interior of Earth is HOT Extrusive Surface of Earth is COOL High Temperatures Lower temperatures allow magma to cool SLOWLY cause the lava to cool QUICKLY Slow cooling allows time for LARGE mineral crystals to form No time for large mineral crystals to form so there are SMALL mineral crystals Composition of Igneous Rocks Texture is not enough to identify an Igneous Rock. Some Igneous Rocks have similar textures. Composition is based on Silicate levels. Silica: Compound made up of silicon and oxygen which geologists use to classify rocks Estimate SILICATE level by COLOR LIGHT COLOR HIGH LEVELS OF SILICA Granite/Rhyolite Gabbro/Basalt LOW LEVELS OF SILICA DARK COLOR Rocks in the World Around Us Rocks in the World Around Us