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Transcript
Rocks and the Rock Cycle As we already learned, rocks are made from minerals and can be classified into 3 major families (or types) based on how they are formed The 3 Families are: Igneous Rocks Sedimentary Rocks Metamorphic Rocks Igneous rocks are formed when magma and hot lava cool and solidify Magma – is melted rock that is found inside and below the Earth’s crust in the Mantle. The Mantle is mostly solid. Extreme heat causes the Mantle to move in currents The Mantle Convection currents in the magma drive plate tectonics. Heat generated from pressure and the radioactive decay of elements deep in the interior of the Earth creates magma Geologists classify igneous rocks based on where they were formed above or below the Earth’s surface. There are 2 types of igneous rocks. Types of Igneous Rocks: Intrusive Rock Extrusive Rock When magma cools and hardens below the Earth’s surface a new rock is formed. Because the rock was formed in the Earth’s surface we call it an Intrusive Rock. Granite is an example of an intrusive rock (Igneous Rock) because it is formed very slowly and deep in the Earth’s Crust. Extrusive Rocks are formed when lava cools on the Earth’s surface. Lava is the name for magma once it breaks through the Earth’s surface during a volcanic eruption. Example: Basalt http://www.youtube.com/watch?v=nuIercRAxQU&feature=related Sedimentary Rocks are made from sediments which are loose materials such as bits of minerals, rock and plant and animals remains. The sediment becomes packed and cemented together Sedimentary Rocks make up about 75% of the rocks on the Earth’s Surface because Igneous Rocks mostly occur below the Earth’s Surface Over many years the rock sediments begin to settle and pile up usually near lakes and oceans As the sediment settles on top of other sediment, the rock begins to take on a layered appearance. These layers are called beds As the layers of sediment begin to form on top of each other, their weight causes the rocks to become compacted (squeezed together) or Lithification In some rocks the minerals dissolve in the water creating a natural cement that holds the rock together This process is known as Compaction Lithification Limestone is the most common type of sedimentary rock. It is a very unique rock because it is formed from large amounts of sediment and the remains of fossils (such as mussels and snails) Fossilized limestone in North Carolina http://www.youtube.com/watch?v=Aqy-p41VpKU&feature=related Metamorphic Rocks are created under the Earth’s surface when extremely high pressure and heat cause the rock to “change form” Slate and Marble are two examples of metamorphic rocks Slate Marble We have learned that Igneous Rocks are formed when magma or lava cools Sedimentary Rocks are formed from sediments are compacted and cemented together Metamorphic Rocks are formed from both igneous and sedimentary rocks which have undergone high pressure and heat Because rocks are continually changing on an ongoing basis we call this process “The Rock Cycle” As we have learned, sediment is formed when larger rocks have broken or become worn away from a natural process known as weathering. Mechanical Weathering is defined by rocks that are physically broken up by things such as gravity, weather and erosion. Example: When a rock falls off a cliff, gravity pulls it to the ground and parts can become broken off. Erosion is a type of mechanical weathering that “wears away” and deposition is a process that build up by blowing or “depositing” sediments from one place to another Erosion Deposition Grand Canyon Arizona Devils Tower Wyoming Chemical Weathering is a breakdown of minerals due to a chemical reaction with water, chemicals dissolved in the water, or with gases in the air. Example: Acid Rain – can react with some rocks Photo: Limestone is weathered due to rainwater Amphibolite Metamorphic Rock (from Basalt) Gneiss Metamorphic Rock (from Granite) Limestone Sedimentary Rock Shale Sedimentary Rock Slate Metamorphic Rock ( from Shale)