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 below the Earth’s crust. Even though the Earth’s mantle is solid, magma can sometimes be found in pockets

 Geologists classify igneous rocks based on where they were formed above or below the Earth’s surfce. 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

 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)  In some rocks the minerals dissolve in the water creating a natural cement that holds the rock together

 This process is known as Compaction

 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

 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 SlateMarble

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 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 sediments from one place to another ErosionDeposition

 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

 Biological Weathering is the when rocks are broken physically or chemically due to living organisms (plants, animals, bacteria, and fungi).