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Chapter 4 Rocks What is a rock? A rock is a mixture of minerals, minerialoids, glass or organic matter. Types of Rocks •Sedimentary •Igneous •Metamorphic How are rocks formed? • Rocks are formed through a series of processes that transforms Earth materials back and forth from the three types of rocks. • This process is called the rock cycle. ROCK CYCLE • Shows the three types of rock and they are formed. • Factors involved in rock formationweathering, erosion, heat, pressure • Processes that form rock – compaction, cementation, melting, cooling • Ever-changing processes moving from one type of rock to another. IGNEOUS ROCKS • Rocks that are formed either molten material from a volcano or from deep inside the Earth’s surface. Two Types of molten material • Lava • Magma Both can reach temps of 1400oC. What is Lava? • Lava- the molten material that reaches the Earth’s surface after a volcanic eruption. It is pushed to the surface due to intense heat and pressure. • The outside air or water cools the materials forming rocks. What is magma? • Magma – molten material found beneath the Earth’s surface. • Found about 60km to 200 km below the surface. • Radioactive elements and intense pressure melts rocks forming magma. • Less dense than the solid rock so it pushed to the surface. Two types of igneous rock • Intrusive – rocks that are formed from magma beneath the Earth’s surface. • Extrusive – rocks that are formed when lava cools on or near the Earth surface. Intrusive Igneous Rocks • Formed from large mineral grains • Are found when rock and soil are removed or when it pushed to the surface or forces in Earth have pushed them to the surface. Extrusive Igneous Rocks • Lava flows to the surface of the Earth and is cooled by air or moisture. • Cools quickly so mineral grains are small. • Typically fine-grained in texture. Classification of Igneous Rocks • Igneous rock is classified by the three magma that formed them. • Three types of magma is basaltic, granitic, and andesitic. Basic Igneous Rock Textures • Fine – grained: Crystals too small to be seen without the unaided eye. • Coarse- grained: Crystals large enough to be seen by the unaided eye • Glassy: Brittle glossy crystals due to quick cooling. • Porphyritic: Large crystals embedded in a cluster of small crystals. Weathering • Day-in and day-out influences of the atmosphere. • Changing temperature, Wind, Humidity, and organic matter. • Causes slow disintegration and rock decomposition.