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Rocks What is a rock? • Rock- naturally formed, consolidated materials composed of one or more minerals. • There are 3 types of rocks: • Igneous • Sedimentary • Metamorphic Igneous Rocks What are Igneous Rocks? • Magma vs. Lava • Magma- molten rock below the Earth’s surface. • Lava- magma on the Earth’s surface. • Igneous Rock- rocks made from cooling magma or lava. • They can be intrusive or extrusive. Intrusive vs. Extrusive • Intrusive Igneous Rocks- a rock that forms below the Earth’s surface. • Normally made from magma • Extrusive Igneous Rocks- a rock formed on the Earth’s surface. • Normally made from lava. Extrusive rock The white rock is intrusive. Intrusive Igneous Rocks • We cannot see these rocks be formed. • They typically have large crystal minerals. • The rock itself can give you a lot of information about how it was formed. Extrusive Igneous Rocks • You can see them form: • Lava flow • Ash Flow • Lava that cools down very quickly so all you see is ask coming out • Pyroclastic Flow • Clouds flowing downhill like a huge avalanche. • Data from these rocks can be used to interpret ancient volcanic activity. Igneous Rock Textures • The crystal size of the rock is related to the speed of the rock cooling. • Fast gives you small crystals and slow cooling gives you large crystals. • Also the rocks can appear: • Glassy- look like a piece of glass. • From the magma/lava cooling too quickly. • Vesicular- has air bubbles in it. • From air bubbles getting trapped in the magma/lava. This is glassy and fragmental. • Fragmental- they look jagged and angular. This is vesicular. Igneous Rock Composition • The composition is based on the amount of silica in the Felsic rock. • Felsic- has the most silica Mafic • Light colored • Mafic- 50% silica Intermediate • Dark colored • Intermediate- Halfway between felsic and mafic • Tend to be gray • Ultramafic- Less than 45% silica • Green in color Ultramafic Classifying Igneous Rocks • To classify an igneous rock, you need 2 basic elements. • Texture • Composition • Texture + composition=rock name • When you classify the rock, you can determine what minerals present. Some Examples of Common Igneous Rocks Rhyolite Granite Obsidian Basalt Andesite Pumice Watch this Have your rock graphic organizer out and fill it in as the video goes on. We will discuss it at the end of the video. https://www.youtube.com/watch?v=aCnAF1Opt8M
